Tiamat, Genesis Mother

At the beginning of each end step, put a
slime counter on each creature you don't control. Creatures you don't control get
-1/-1 for each slime counter on them.
Whenever a creature you don't control with
a slime counter on it dies, create a 1/1 black Slug creature token.
{u}{b}: Sacrifice a Slug: Draw a card.