Get In The Bucket Mod (Fabric)

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Mod for Minecraft that allows mobs to be placed in a bucket.

Right-clicking all mobs will give you a bucket with that mob.

To add Entities' NBT with commands, throw it into EntityData tag.

In Creative Mode, picking up mobs will delete them and placing works the same as with spawn eggs.

Modded entities use a generic "Bucket of Entity" item.