diff --git a/build/entity.rs b/build/entity.rs
new file mode 100644
index 0000000..0281ff6
--- /dev/null
+++ b/build/entity.rs
@@ -0,0 +1,1624 @@
+//! See: <https://wiki.vg/Entity_metadata>
+
+#![allow(unused)]
+
+struct Class {
+    name: &'static str,
+    inherit: Option<&'static Class>,
+    fields: &'static [Field],
+}
+
+struct Field {
+    name: &'static str,
+    typ: Type,
+}
+
+/// Each variant contains the default value for the field.
+enum Type {
+    BitFields(&'static [BitField]),
+    Byte(u8),
+    VarInt(i32),
+    Float(f32),
+    String(&'static str),
+    Text,
+    OptText(Option<&'static str>),
+    Slot,
+    Bool(bool),
+    Rotations(f32, f32, f32),
+    BlockPos(i32, i32, i32),
+    OptPosition(Option<(i32, i32, i32)>),
+    Direction(Direction),
+    OptUuid,
+    OptBlockId,
+    Nbt,
+    Particle,
+    VillagerData,
+    OptVarInt,
+    Pose,
+    OptBlockPos, // TODO: What is this type?
+    // ==== Specialized ==== //
+    OptEntityId,
+    BoatType,
+    MainHand,
+}
+
+enum Direction {
+    Down,
+    Up,
+    North,
+    South,
+    West,
+    East,
+}
+
+struct BitField {
+    name: &'static str,
+    offset: u8,
+}
+
+const BASE_ENTITY: Class = Class {
+    name: "entity_base",
+    inherit: None,
+    fields: &[
+        Field {
+            name: "entity_base_bits",
+            typ: Type::BitFields(&[
+                BitField {
+                    name: "on_fire",
+                    offset: 0,
+                },
+                BitField {
+                    name: "crouching",
+                    offset: 1,
+                },
+                BitField {
+                    name: "sprinting",
+                    offset: 3, // Skipping unused field
+                },
+                BitField {
+                    name: "swimming",
+                    offset: 4,
+                },
+                BitField {
+                    name: "invisible",
+                    offset: 5,
+                },
+                BitField {
+                    name: "glowing",
+                    offset: 6,
+                },
+                BitField {
+                    name: "elytra_flying",
+                    offset: 7,
+                },
+            ]),
+        },
+        Field {
+            name: "air_ticks",
+            typ: Type::VarInt(300),
+        },
+        Field {
+            name: "custom_name",
+            typ: Type::OptText(None),
+        },
+        Field {
+            name: "custom_name_visible",
+            typ: Type::Bool(false),
+        },
+        Field {
+            name: "silent",
+            typ: Type::Bool(false),
+        },
+        Field {
+            name: "no_gravity",
+            typ: Type::Bool(false),
+        },
+        Field {
+            name: "pose",
+            typ: Type::Pose,
+        },
+        Field {
+            name: "frozen_ticks",
+            typ: Type::VarInt(0),
+        },
+    ],
+};
+
+const ABSTRACT_ARROW: Class = Class {
+    name: "abstract_arrow",
+    inherit: Some(&BASE_ENTITY),
+    fields: &[
+        Field {
+            name: "abstract_arrow_bits",
+            typ: Type::BitFields(&[
+                BitField {
+                    name: "critical",
+                    offset: 0,
+                },
+                BitField {
+                    name: "noclip",
+                    offset: 1,
+                },
+            ]),
+        },
+        Field {
+            name: "piercing_level",
+            typ: Type::Byte(0),
+        },
+    ],
+};
+
+const LIVING_ENTITY: Class = Class {
+    name: "living_entity",
+    inherit: Some(&BASE_ENTITY),
+    fields: &[
+        Field {
+            name: "living_entity_bits",
+            typ: Type::BitFields(&[
+                BitField {
+                    name: "hand_active",
+                    offset: 0,
+                },
+                BitField {
+                    name: "active_hand",
+                    offset: 1,
+                },
+                BitField {
+                    name: "riptide_spin_attack",
+                    offset: 2,
+                },
+            ]),
+        },
+        Field {
+            name: "health",
+            typ: Type::Float(1.0),
+        },
+        Field {
+            name: "potion_effect_color",
+            typ: Type::VarInt(0), // TODO: potion effect color type
+        },
+        Field {
+            name: "potion_effect_ambient",
+            typ: Type::Bool(false),
+        },
+        Field {
+            name: "arrow_count",
+            typ: Type::VarInt(0),
+        },
+        Field {
+            name: "bee_stinger_count",
+            typ: Type::VarInt(0),
+        },
+        Field {
+            name: "bed_sleeping_position",
+            typ: Type::OptBlockPos,
+        },
+    ],
+};
+
+const MOB: Class = Class {
+    name: "mob",
+    inherit: Some(&LIVING_ENTITY),
+    fields: &[Field {
+        name: "mob_bits",
+        typ: Type::BitFields(&[
+            BitField {
+                name: "ai_disabled",
+                offset: 0,
+            },
+            BitField {
+                name: "left_handed",
+                offset: 1,
+            },
+            BitField {
+                name: "aggressive",
+                offset: 2,
+            },
+        ]),
+    }],
+};
+
+const AMBIENT_CREATURE: Class = Class {
+    name: "ambient_creature",
+    inherit: Some(&MOB),
+    fields: &[],
+};
+
+const PATHFINDER_MOB: Class = Class {
+    name: "pathfinder_mob",
+    inherit: Some(&MOB),
+    fields: &[],
+};
+
+const WATER_ANIMAL: Class = Class {
+    name: "water_animal",
+    inherit: Some(&PATHFINDER_MOB),
+    fields: &[],
+};
+
+const ABSTRACT_FISH: Class = Class {
+    name: "abstract_fish",
+    inherit: Some(&WATER_ANIMAL),
+    fields: &[Field {
+        name: "from_bucket",
+        typ: Type::Bool(false),
+    }],
+};
+
+const AGEABLE_MOB: Class = Class {
+    name: "ageable_mob",
+    inherit: Some(&PATHFINDER_MOB),
+    fields: &[Field {
+        name: "is_baby",
+        typ: Type::Bool(false),
+    }],
+};
+
+const ANIMAL: Class = Class {
+    name: "animal",
+    inherit: Some(&PATHFINDER_MOB),
+    fields: &[],
+};
+
+const ABSTRACT_HORSE: Class = Class {
+    name: "abstract_horse",
+    inherit: Some(&ANIMAL),
+    fields: &[
+        Field {
+            name: "horse_bits",
+            typ: Type::BitFields(&[
+                BitField {
+                    name: "tame",
+                    offset: 1, // Skip unused
+                },
+                BitField {
+                    name: "saddled",
+                    offset: 2,
+                },
+                BitField {
+                    name: "bred",
+                    offset: 3,
+                },
+                BitField {
+                    name: "eating",
+                    offset: 4,
+                },
+                BitField {
+                    name: "rearing",
+                    offset: 5,
+                },
+                BitField {
+                    name: "mouth_open",
+                    offset: 6,
+                },
+            ]),
+        },
+        Field {
+            name: "owner",
+            typ: Type::OptUuid,
+        },
+    ],
+};
+
+const CHESTED_HORSE: Class = Class {
+    name: "chested_horse",
+    inherit: Some(&ABSTRACT_HORSE),
+    fields: &[Field {
+        name: "has_chest",
+        typ: Type::Bool(false),
+    }],
+};
+
+const COW: Class = Class {
+    name: "cow",
+    inherit: Some(&ANIMAL),
+    fields: &[],
+};
+
+const TAMEABLE_ANIMAL: Class = Class {
+    name: "tameable_animal",
+    inherit: Some(&ANIMAL),
+    fields: &[Field {
+        name: "tameable_animal_bits",
+        typ: Type::BitFields(&[
+            BitField {
+                name: "sitting",
+                offset: 0,
+            },
+            BitField {
+                name: "tamed",
+                offset: 2, // Skip unused.
+            },
+        ]),
+    }],
+};
+
+const ABSTRACT_VILLAGER: Class = Class {
+    name: "abstract_villager",
+    inherit: Some(&AGEABLE_MOB),
+    fields: &[Field {
+        name: "head_shake_timer",
+        typ: Type::VarInt(0),
+    }],
+};
+
+const ABSTRACT_GOLEM: Class = Class {
+    name: "abstract_golem",
+    inherit: Some(&PATHFINDER_MOB),
+    fields: &[],
+};
+
+const MONSTER: Class = Class {
+    name: "monster",
+    inherit: Some(&PATHFINDER_MOB),
+    fields: &[],
+};
+
+const BASE_PIGLIN: Class = Class {
+    name: "base_piglin",
+    inherit: Some(&MONSTER),
+    fields: &[Field {
+        name: "zombification_immune",
+        typ: Type::Bool(false),
+    }],
+};
+
+const GUARDIAN: Class = Class {
+    name: "guardian",
+    inherit: Some(&MONSTER),
+    fields: &[
+        Field {
+            name: "retracting_spikes",
+            typ: Type::Bool(false),
+        },
+        Field {
+            name: "target",
+            typ: Type::OptEntityId,
+        },
+    ],
+};
+
+const RAIDER: Class = Class {
+    name: "raider",
+    inherit: Some(&MONSTER),
+    fields: &[Field {
+        name: "celebrating",
+        typ: Type::Bool(false),
+    }],
+};
+
+const ABSTRACT_ILLAGER: Class = Class {
+    name: "abstract_illager",
+    inherit: Some(&RAIDER),
+    fields: &[],
+};
+
+const SPELLCASTER_ILLAGER: Class = Class {
+    name: "spellcaster_illager",
+    inherit: Some(&ABSTRACT_ILLAGER),
+    fields: &[Field {
+        name: "spellcaster_state",
+        typ: Type::Byte(0), /* TODO: Spell (0: none, 1: summon vex, 2: attack, 3: wololo, 4:
+                             * disappear, 5: blindness) */
+    }],
+};
+
+const ABSTRACT_SKELETON: Class = Class {
+    name: "abstract_skeleton",
+    inherit: Some(&MONSTER),
+    fields: &[],
+};
+
+const SPIDER: Class = Class {
+    name: "spider",
+    inherit: Some(&MONSTER),
+    fields: &[Field {
+        name: "spider_bits",
+        typ: Type::BitFields(&[BitField {
+            name: "climbing",
+            offset: 0,
+        }]),
+    }],
+};
+
+const ZOMBIE: Class = Class {
+    name: "zombie",
+    inherit: Some(&MONSTER),
+    fields: &[Field {
+        name: "baby",
+        typ: Type::Bool(false),
+    }],
+};
+
+const FLYING: Class = Class {
+    name: "flying",
+    inherit: Some(&MOB),
+    fields: &[],
+};
+
+const ABSTRACT_MINECART: Class = Class {
+    name: "abstract minecart",
+    inherit: Some(&BASE_ENTITY),
+    fields: &[
+        Field {
+            name: "shaking_power",
+            typ: Type::VarInt(0),
+        },
+        Field {
+            name: "shaking_direction",
+            typ: Type::VarInt(1), // TODO: Refined type?
+        },
+        Field {
+            name: "shaking_multiplier",
+            typ: Type::Float(0.0),
+        },
+        Field {
+            name: "custom_block_id",
+            typ: Type::VarInt(0), // TODO: is this a BlockState?
+        },
+        Field {
+            name: "custom_block_y_pos",
+            typ: Type::VarInt(6), // TODO: measured in 16ths of a block. Refined type?
+        },
+        Field {
+            name: "show_custom_block",
+            typ: Type::Bool(false),
+        },
+    ],
+};
+
+const ABSTRACT_MINECART_CONTAINER: Class = Class {
+    name: "abstract_minecart_container",
+    inherit: Some(&ABSTRACT_MINECART),
+    fields: &[],
+};
+
+const ENTITIES: &[Class] = &[
+    Class {
+        name: "experience_orb",
+        inherit: None,
+        fields: &[],
+    },
+    Class {
+        name: "painting",
+        inherit: None,
+        fields: &[],
+    },
+    Class {
+        name: "thrown_egg",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "item",
+            typ: Type::Slot,
+        }],
+    },
+    Class {
+        name: "thrown_ender_pearl",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "item",
+            typ: Type::Slot,
+        }],
+    },
+    Class {
+        name: "thrown_experience_bottle",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "item",
+            typ: Type::Slot,
+        }],
+    },
+    Class {
+        name: "thrown_potion",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "potion",
+            typ: Type::Slot,
+        }],
+    },
+    Class {
+        name: "snowball",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "item",
+            typ: Type::Slot,
+        }],
+    },
+    Class {
+        name: "eye_of_ender",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "item",
+            typ: Type::Slot,
+        }],
+    },
+    Class {
+        name: "falling_block",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "spawn_position",
+            typ: Type::BlockPos(0, 0, 0),
+        }],
+    },
+    Class {
+        name: "area_effect_cloud",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[
+            Field {
+                name: "radius",
+                typ: Type::Float(0.5),
+            },
+            Field {
+                name: "color",
+                typ: Type::VarInt(0),
+            },
+            Field {
+                name: "ignore_radius",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "particle",
+                typ: Type::Particle,
+            },
+        ],
+    },
+    Class {
+        name: "fishing_hook",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[
+            Field {
+                name: "hooked_entity",
+                typ: Type::OptEntityId,
+            },
+            Field {
+                name: "catchable",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "arrow",
+        inherit: Some(&ABSTRACT_ARROW),
+        fields: &[Field {
+            name: "color",
+            typ: Type::VarInt(-1), // TODO: custom type
+        }],
+    },
+    Class {
+        name: "spectral_arrow",
+        inherit: Some(&ABSTRACT_ARROW),
+        fields: &[],
+    },
+    Class {
+        name: "thrown_trident",
+        inherit: Some(&ABSTRACT_ARROW),
+        fields: &[
+            Field {
+                name: "loyalty_level",
+                typ: Type::VarInt(0),
+            },
+            Field {
+                name: "enchantment_glint",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "boat",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[
+            Field {
+                name: "last_hit_ticks",
+                typ: Type::VarInt(0),
+            },
+            Field {
+                name: "forward_direction",
+                typ: Type::VarInt(1), // TODO: direction enum?
+            },
+            Field {
+                name: "damage_taken",
+                typ: Type::Float(0.0),
+            },
+            Field {
+                name: "typ",
+                typ: Type::BoatType,
+            },
+            Field {
+                name: "left_paddle_turning",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "right_paddle_turning",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "splash_timer",
+                typ: Type::VarInt(0),
+            },
+        ],
+    },
+    Class {
+        name: "end_crystal",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[
+            Field {
+                name: "beam_target",
+                typ: Type::OptBlockPos,
+            },
+            Field {
+                name: "show_bottom",
+                typ: Type::Bool(true),
+            },
+        ],
+    },
+    Class {
+        name: "dragon_fireball",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[],
+    },
+    Class {
+        name: "small_fireball",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "item",
+            typ: Type::Slot,
+        }],
+    },
+    Class {
+        name: "fireball",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "item",
+            typ: Type::Slot,
+        }],
+    },
+    Class {
+        name: "wither_skull",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "invulnerable",
+            typ: Type::Bool(false),
+        }],
+    },
+    Class {
+        name: "firework_rocket",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[
+            Field {
+                name: "info",
+                typ: Type::Slot,
+            },
+            Field {
+                name: "used_by",
+                typ: Type::OptEntityId,
+            },
+            Field {
+                name: "shot_at_angle",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "item_frame",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[
+            Field {
+                name: "item",
+                typ: Type::Slot,
+            },
+            Field {
+                name: "rotation",
+                typ: Type::VarInt(0), // TODO: Direction enum?
+            },
+        ],
+    },
+    Class {
+        // TODO: How is glow item frame defined? This is a guess.
+        name: "glow_item_frame",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[
+            Field {
+                name: "item",
+                typ: Type::Slot,
+            },
+            Field {
+                name: "rotation",
+                typ: Type::VarInt(0), // TODO: Direction enum?
+            },
+        ],
+    },
+    Class {
+        name: "player",
+        inherit: Some(&LIVING_ENTITY),
+        fields: &[
+            Field {
+                name: "additional_hearts",
+                typ: Type::Float(0.0),
+            },
+            Field {
+                name: "score",
+                typ: Type::VarInt(0),
+            },
+            Field {
+                name: "displayed_skin_parts",
+                typ: Type::BitFields(&[
+                    BitField {
+                        name: "cape_enabled",
+                        offset: 0,
+                    },
+                    BitField {
+                        name: "jacket_enabled",
+                        offset: 1,
+                    },
+                    BitField {
+                        name: "left_sleeve_enabled",
+                        offset: 2,
+                    },
+                    BitField {
+                        name: "right_sleeve_enabled",
+                        offset: 3,
+                    },
+                    BitField {
+                        name: "left_pants_leg_enabled",
+                        offset: 4,
+                    },
+                    BitField {
+                        name: "right_pants_leg_enabled",
+                        offset: 5,
+                    },
+                    BitField {
+                        name: "hat_enabled",
+                        offset: 6,
+                    },
+                ]),
+            },
+            Field {
+                name: "main_hand",
+                typ: Type::MainHand,
+            },
+            Field {
+                name: "left_shoulder_entity_data",
+                typ: Type::Nbt,
+            },
+            Field {
+                name: "right_shoulder_entity_data",
+                typ: Type::Nbt,
+            },
+        ],
+    },
+    Class {
+        name: "armor_stand",
+        inherit: Some(&LIVING_ENTITY),
+        fields: &[
+            Field {
+                name: "armor_stand_bits",
+                typ: Type::BitFields(&[
+                    BitField {
+                        name: "small",
+                        offset: 0,
+                    },
+                    BitField {
+                        name: "has_arms",
+                        offset: 1,
+                    },
+                    BitField {
+                        name: "no_baseplate",
+                        offset: 2,
+                    },
+                    BitField {
+                        name: "is_marker",
+                        offset: 3,
+                    },
+                ]),
+            },
+            Field {
+                name: "head_rotation",
+                typ: Type::Rotations(0.0, 0.0, 0.0),
+            },
+            Field {
+                name: "body_rotation",
+                typ: Type::Rotations(0.0, 0.0, 0.0),
+            },
+            Field {
+                name: "left_arm_rotation",
+                typ: Type::Rotations(-10.0, 0.0, -10.0),
+            },
+            Field {
+                name: "right_arm_rotation",
+                typ: Type::Rotations(-15.0, 0.0, -10.0),
+            },
+            Field {
+                name: "left_leg_rotation",
+                typ: Type::Rotations(-1.0, 0.0, -1.0),
+            },
+            Field {
+                name: "right_leg_rotation",
+                typ: Type::Rotations(1.0, 0.0, 1.0),
+            },
+        ],
+    },
+    Class {
+        name: "bat",
+        inherit: Some(&AMBIENT_CREATURE),
+        fields: &[Field {
+            name: "bat_bits",
+            typ: Type::BitFields(&[BitField {
+                name: "hanging",
+                offset: 0,
+            }]),
+        }],
+    },
+    Class {
+        name: "squid",
+        inherit: Some(&WATER_ANIMAL),
+        fields: &[],
+    },
+    Class {
+        // TODO: How is glow squid defined? This is a guess.
+        name: "glow_squid",
+        inherit: Some(&WATER_ANIMAL),
+        fields: &[],
+    },
+    Class {
+        name: "dolphin",
+        inherit: Some(&WATER_ANIMAL),
+        fields: &[
+            Field {
+                name: "treasure_position",
+                typ: Type::BlockPos(0, 0, 0),
+            },
+            Field {
+                name: "has_fish",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "moisture_level",
+                typ: Type::VarInt(2400),
+            },
+        ],
+    },
+    Class {
+        name: "cod",
+        inherit: Some(&ABSTRACT_FISH),
+        fields: &[],
+    },
+    Class {
+        name: "puffer_fish",
+        inherit: Some(&ABSTRACT_FISH),
+        fields: &[Field {
+            name: "puff_state",
+            typ: Type::VarInt(0), // TODO: PuffState in the range [0, 2]. (Bounded int?)
+        }],
+    },
+    Class {
+        name: "salmon",
+        inherit: Some(&ABSTRACT_FISH),
+        fields: &[],
+    },
+    Class {
+        name: "tropical_fish",
+        inherit: Some(&ABSTRACT_FISH),
+        fields: &[Field {
+            name: "variant",
+            typ: Type::VarInt(0), // TODO: TropicalFishVariant enum
+        }],
+    },
+    Class {
+        name: "horse",
+        inherit: Some(&ABSTRACT_HORSE),
+        fields: &[Field {
+            name: "variant",
+            typ: Type::VarInt(0), // TODO: HorseVariant enum
+        }],
+    },
+    Class {
+        name: "zombie_horse",
+        inherit: Some(&ABSTRACT_HORSE),
+        fields: &[],
+    },
+    Class {
+        name: "skeleton_horse",
+        inherit: Some(&ABSTRACT_HORSE),
+        fields: &[],
+    },
+    Class {
+        name: "donkey",
+        inherit: Some(&CHESTED_HORSE),
+        fields: &[],
+    },
+    Class {
+        name: "llama",
+        inherit: Some(&CHESTED_HORSE),
+        fields: &[
+            Field {
+                name: "strength",
+                typ: Type::VarInt(0), // TODO: upper bound?
+            },
+            Field {
+                name: "carpet_color",
+                typ: Type::VarInt(-1), // TODO: Carpet color enum.
+            },
+            Field {
+                name: "variant",
+                typ: Type::VarInt(0), // TODO: Llama variant enum.
+            },
+        ],
+    },
+    Class {
+        name: "trader_llama",
+        inherit: None, // TODO: really?
+        fields: &[],
+    },
+    Class {
+        name: "mule",
+        inherit: Some(&CHESTED_HORSE),
+        fields: &[],
+    },
+    Class {
+        name: "axolotl",
+        inherit: Some(&ANIMAL),
+        fields: &[
+            Field {
+                name: "variant",
+                typ: Type::VarInt(0), // TODO: AxolotlVariant enum.
+            },
+            Field {
+                name: "playing_dead",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "from_bucket",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "bee",
+        inherit: Some(&ANIMAL),
+        fields: &[
+            Field {
+                name: "bee_bits",
+                typ: Type::BitFields(&[
+                    BitField {
+                        name: "angry",
+                        offset: 1, // Skip unused.
+                    },
+                    BitField {
+                        name: "stung",
+                        offset: 2,
+                    },
+                    BitField {
+                        name: "nectar",
+                        offset: 3,
+                    },
+                ]),
+            },
+            Field {
+                name: "anger_ticks",
+                typ: Type::VarInt(0),
+            },
+        ],
+    },
+    Class {
+        name: "fox",
+        inherit: Some(&ANIMAL),
+        fields: &[
+            Field {
+                name: "variant",
+                typ: Type::VarInt(0), // TODO: 0 for red, 1 for snow
+            },
+            Field {
+                name: "fox_bits",
+                typ: Type::BitFields(&[
+                    BitField {
+                        name: "sitting",
+                        offset: 0,
+                    },
+                    BitField {
+                        name: "",
+                        offset: 2, // Skip unused
+                    },
+                ]),
+            },
+            // TODO: what are these UUIDs?
+            Field {
+                name: "first_uuid",
+                typ: Type::OptUuid,
+            },
+            Field {
+                name: "second_uuid",
+                typ: Type::OptUuid,
+            },
+        ],
+    },
+    Class {
+        name: "ocelot",
+        inherit: Some(&ANIMAL),
+        fields: &[Field {
+            name: "trusting",
+            typ: Type::Bool(false),
+        }],
+    },
+    Class {
+        name: "panda",
+        inherit: Some(&ANIMAL),
+        fields: &[
+            Field {
+                name: "breed_timer",
+                typ: Type::VarInt(0),
+            },
+            Field {
+                name: "sneeze_timer",
+                typ: Type::VarInt(0),
+            },
+            Field {
+                name: "eat_timer",
+                typ: Type::VarInt(0),
+            },
+            Field {
+                name: "main_gene",
+                typ: Type::Byte(0),
+            },
+            Field {
+                name: "hidden_gene",
+                typ: Type::Byte(0),
+            },
+            Field {
+                name: "panda_bits",
+                typ: Type::BitFields(&[
+                    BitField {
+                        name: "sneezing",
+                        offset: 1, // Skip unused.
+                    },
+                    BitField {
+                        name: "rolling",
+                        offset: 2,
+                    },
+                    BitField {
+                        name: "sitting",
+                        offset: 3,
+                    },
+                    BitField {
+                        name: "on_back",
+                        offset: 4,
+                    },
+                ]),
+            },
+        ],
+    },
+    Class {
+        name: "pig",
+        inherit: Some(&ANIMAL),
+        fields: &[
+            Field {
+                name: "has_saddle",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "boost_timer",
+                typ: Type::VarInt(0),
+            },
+        ],
+    },
+    Class {
+        name: "rabbit",
+        inherit: Some(&ANIMAL),
+        fields: &[Field {
+            name: "variant",
+            typ: Type::VarInt(0), // TODO: rabbit variant enum.
+        }],
+    },
+    Class {
+        name: "turtle",
+        inherit: Some(&ANIMAL),
+        fields: &[
+            Field {
+                name: "home_position",
+                typ: Type::BlockPos(0, 0, 0),
+            },
+            Field {
+                name: "has_egg",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "laying_egg",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "travel_pos",
+                typ: Type::BlockPos(0, 0, 0),
+            },
+            Field {
+                name: "going_home",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "travelling",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "polar_bear",
+        inherit: Some(&ANIMAL),
+        fields: &[Field {
+            name: "standing_up",
+            typ: Type::Bool(true),
+        }],
+    },
+    Class {
+        name: "chicken",
+        inherit: Some(&ANIMAL),
+        fields: &[],
+    },
+    COW,
+    Class {
+        name: "hoglin",
+        inherit: Some(&ANIMAL),
+        fields: &[Field {
+            name: "zombification_immune",
+            typ: Type::Bool(false),
+        }],
+    },
+    Class {
+        name: "mooshroom",
+        inherit: Some(&COW),
+        fields: &[Field {
+            name: "variant",
+            typ: Type::String("red"), // TODO: "red" or "brown" enum.
+        }],
+    },
+    Class {
+        name: "sheep",
+        inherit: Some(&ANIMAL),
+        fields: &[Field {
+            name: "sheep_state",
+            typ: Type::Byte(0), // TODO: sheep state type.
+        }],
+    },
+    Class {
+        name: "strider",
+        inherit: Some(&ANIMAL),
+        fields: &[
+            Field {
+                name: "boost_timer",
+                typ: Type::VarInt(0),
+            },
+            Field {
+                name: "shaking",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "saddle",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "cat",
+        inherit: Some(&TAMEABLE_ANIMAL),
+        fields: &[
+            Field {
+                name: "variant",
+                typ: Type::VarInt(1), // TODO: cat variant enum.
+            },
+            Field {
+                name: "lying",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "relaxed",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "collar_color",
+                typ: Type::VarInt(14), // TODO: dye color enum.
+            },
+        ],
+    },
+    Class {
+        name: "wolf",
+        inherit: Some(&TAMEABLE_ANIMAL),
+        fields: &[
+            Field {
+                name: "begging",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "collar_color", // TODO: dye color enum
+                typ: Type::VarInt(14),
+            },
+            Field {
+                name: "anger_timer",
+                typ: Type::VarInt(0),
+            },
+        ],
+    },
+    Class {
+        name: "parrot",
+        inherit: Some(&TAMEABLE_ANIMAL),
+        fields: &[Field {
+            name: "variant",
+            typ: Type::VarInt(0), // TODO: parrot variant enum.
+        }],
+    },
+    Class {
+        name: "villager",
+        inherit: Some(&ABSTRACT_VILLAGER),
+        fields: &[Field {
+            name: "villager_data",
+            typ: Type::VillagerData,
+        }],
+    },
+    Class {
+        name: "wandering_trader",
+        inherit: Some(&ABSTRACT_VILLAGER),
+        fields: &[],
+    },
+    Class {
+        name: "iron_golem",
+        inherit: Some(&ABSTRACT_GOLEM),
+        fields: &[Field {
+            name: "iron_golem_bits",
+            typ: Type::BitFields(&[BitField {
+                name: "player_created",
+                offset: 0,
+            }]),
+        }],
+    },
+    Class {
+        name: "snow_golem",
+        inherit: Some(&ABSTRACT_GOLEM),
+        fields: &[Field {
+            name: "snow_golem_bits",
+            typ: Type::BitFields(&[BitField {
+                name: "pumpkin_hat",
+                offset: 4,
+                // TODO: should default to true.
+            }]),
+        }],
+    },
+    Class {
+        name: "shulker",
+        inherit: Some(&ABSTRACT_GOLEM),
+        fields: &[
+            Field {
+                name: "attach_face",
+                typ: Type::Direction(Direction::Down),
+            },
+            Field {
+                name: "attachment_position",
+                typ: Type::OptPosition(None),
+            },
+            Field {
+                name: "shield_height",
+                typ: Type::Byte(0),
+            },
+            Field {
+                name: "color",
+                typ: Type::Byte(10), // TODO: dye color enum
+            },
+        ],
+    },
+    Class {
+        name: "piglin",
+        inherit: Some(&BASE_PIGLIN),
+        fields: &[
+            Field {
+                name: "baby",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "charging_crossbow",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "dancing",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "piglin_brute",
+        inherit: Some(&BASE_PIGLIN),
+        fields: &[],
+    },
+    Class {
+        name: "blaze",
+        inherit: Some(&MONSTER),
+        fields: &[Field {
+            name: "blaze_bits",
+            typ: Type::BitFields(&[BitField {
+                name: "blaze_on_fire", // TODO: better name for this?
+                offset: 0,
+            }]),
+        }],
+    },
+    Class {
+        name: "creeper",
+        inherit: Some(&MONSTER),
+        fields: &[
+            Field {
+                name: "creeper_state",
+                typ: Type::VarInt(-1), // TODO -1 for idle, +1 for fuse.
+            },
+            Field {
+                name: "charged",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "ignited",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "endermite",
+        inherit: Some(&MONSTER),
+        fields: &[],
+    },
+    Class {
+        name: "giant",
+        inherit: Some(&MONSTER),
+        fields: &[],
+    },
+    GUARDIAN,
+    Class {
+        name: "elder_guardian",
+        inherit: Some(&GUARDIAN),
+        fields: &[],
+    },
+    Class {
+        name: "silverfish",
+        inherit: Some(&MONSTER),
+        fields: &[],
+    },
+    Class {
+        name: "vindicator",
+        inherit: Some(&ABSTRACT_ILLAGER),
+        fields: &[],
+    },
+    Class {
+        name: "pillager",
+        inherit: Some(&ABSTRACT_ILLAGER),
+        fields: &[Field {
+            name: "charging",
+            typ: Type::Bool(false),
+        }],
+    },
+    Class {
+        name: "evoker",
+        inherit: Some(&SPELLCASTER_ILLAGER),
+        fields: &[],
+    },
+    Class {
+        name: "illusioner",
+        inherit: Some(&SPELLCASTER_ILLAGER),
+        fields: &[],
+    },
+    Class {
+        name: "ravager",
+        inherit: Some(&RAIDER),
+        fields: &[],
+    },
+    Class {
+        name: "evoker_fanges",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[],
+    },
+    Class {
+        name: "witch",
+        inherit: Some(&RAIDER),
+        fields: &[Field {
+            name: "drinking_potion",
+            typ: Type::Bool(false),
+        }],
+    },
+    Class {
+        name: "vex",
+        inherit: Some(&MONSTER),
+        fields: &[Field {
+            name: "vex_bits",
+            typ: Type::BitFields(&[BitField {
+                name: "attacking",
+                offset: 0,
+            }]),
+        }],
+    },
+    Class {
+        name: "skeleton",
+        inherit: Some(&ABSTRACT_SKELETON),
+        fields: &[],
+    },
+    Class {
+        name: "wither_skeleton",
+        inherit: Some(&ABSTRACT_SKELETON),
+        fields: &[],
+    },
+    Class {
+        name: "stray",
+        inherit: Some(&ABSTRACT_SKELETON),
+        fields: &[],
+    },
+    SPIDER,
+    Class {
+        name: "cave_spider",
+        inherit: Some(&SPIDER), // TODO: does cave_spider inherit from spider?
+        fields: &[],
+    },
+    Class {
+        name: "wither",
+        inherit: Some(&MONSTER),
+        fields: &[
+            // TODO: are these actually OptEntityId, or something else?
+            Field {
+                name: "center_head_target",
+                typ: Type::OptEntityId,
+            },
+            Field {
+                name: "left_head_target",
+                typ: Type::OptEntityId,
+            },
+            Field {
+                name: "right_head_target",
+                typ: Type::OptEntityId,
+            },
+            Field {
+                name: "invulnerable_time",
+                typ: Type::VarInt(0),
+            },
+        ],
+    },
+    Class {
+        name: "zoglin",
+        inherit: Some(&MONSTER),
+        fields: &[Field {
+            name: "baby",
+            typ: Type::Bool(false),
+        }],
+    },
+    ZOMBIE,
+    Class {
+        name: "zombie_villager",
+        inherit: Some(&ZOMBIE),
+        fields: &[
+            Field {
+                name: "converting",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "villager_data",
+                typ: Type::VillagerData,
+            },
+        ],
+    },
+    Class {
+        name: "husk",
+        inherit: Some(&ZOMBIE),
+        fields: &[],
+    },
+    Class {
+        name: "drowned",
+        inherit: Some(&ZOMBIE),
+        fields: &[],
+    },
+    Class {
+        name: "zombified_piglin",
+        inherit: Some(&ZOMBIE),
+        fields: &[],
+    },
+    Class {
+        name: "enderman",
+        inherit: Some(&MONSTER),
+        fields: &[
+            Field {
+                name: "carried_block",
+                typ: Type::OptBlockId,
+            },
+            Field {
+                name: "screaming",
+                typ: Type::Bool(false),
+            },
+            Field {
+                name: "staring",
+                typ: Type::Bool(false),
+            },
+        ],
+    },
+    Class {
+        name: "ender_dragon",
+        inherit: Some(&MOB),
+        fields: &[Field {
+            name: "phase",
+            typ: Type::VarInt(10), // TODO: dragon phase enum
+        }],
+    },
+    Class {
+        name: "ghast",
+        inherit: Some(&FLYING),
+        fields: &[Field {
+            name: "attacking",
+            typ: Type::Bool(false),
+        }],
+    },
+    Class {
+        name: "phantom",
+        inherit: Some(&FLYING),
+        fields: &[Field {
+            name: "size",
+            typ: Type::VarInt(0),
+        }],
+    },
+    Class {
+        name: "slime",
+        inherit: Some(&MOB),
+        fields: &[Field {
+            name: "size",
+            typ: Type::VarInt(1), // TODO: bounds?
+        }],
+    },
+    Class {
+        name: "llama_spit",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[],
+    },
+    Class {
+        name: "minecart",
+        inherit: Some(&ABSTRACT_MINECART),
+        fields: &[],
+    },
+    Class {
+        name: "minecart_hopper",
+        inherit: Some(&ABSTRACT_MINECART_CONTAINER),
+        fields: &[],
+    },
+    Class {
+        name: "minecart_chest",
+        inherit: Some(&ABSTRACT_MINECART_CONTAINER),
+        fields: &[],
+    },
+    Class {
+        name: "minecart_furnace",
+        inherit: Some(&ABSTRACT_MINECART),
+        fields: &[Field {
+            name: "has_fuel",
+            typ: Type::Bool(false),
+        }],
+    },
+    Class {
+        name: "minecart_tnt",
+        inherit: Some(&ABSTRACT_MINECART),
+        fields: &[],
+    },
+    Class {
+        name: "minecart_spawner",
+        inherit: Some(&ABSTRACT_MINECART),
+        fields: &[],
+    },
+    Class {
+        name: "minecart_command_block",
+        inherit: Some(&ABSTRACT_MINECART),
+        fields: &[
+            Field {
+                name: "command",
+                typ: Type::String(""),
+            },
+            Field {
+                name: "last_output",
+                typ: Type::Text,
+            },
+        ],
+    },
+    Class {
+        name: "primed_tnt",
+        inherit: Some(&BASE_ENTITY),
+        fields: &[Field {
+            name: "fuse_timer",
+            typ: Type::VarInt(80),
+        }],
+    },
+];
+
+pub fn build() -> anyhow::Result<()> {
+    Ok(())
+}