Mod that allows mobs to be placed into buckets
Right-clicking all mobs will give you a bucket with that mob.
NBT is saved when an entity is picked up.
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.
Special Thanks to:
sigy4444 - German Translation