Slime

Slimes often spawn in flat worlds. They are large,medium and small. If they killed, they split into sizes. Large slimes to medium slimes when killed they split into small slimes. Small slimes can't attack players. Medium sized slimes damage you when you are in its position.

They drop 0-4 slime balls

Their size can be changed by using command /summon Slime ~ ~ ~ {Size:(choice)}.

Don't spawn too large slimes or minecraft will lag or freeze.