Zac, the Secret Weapon

When Zac, the Secret Weapon enters the battlefield, create two 0/1 green Slime creature
tokens.
Whenever Zac takes damage, create a 0/1 green
Slime creature token.
When Zac, the Secret Weapon dies, if there are
four or more Slime creature tokens on the
battlefield under your control, sacrifice them and
return Zac to the battlefield under your control at
the beginning of the next end step.