Brood Queen

Flying, Deathtouch
When Brood Queen enters the battlefield, create two 1/1 green Infected creature tokens with “At the beginning of your end step, sacrifice this creature unless you control a Zerg or a creature with infect.”
{b}, {t}: Sacrifice a Zerg creature you control. Create a 3/3 black Zerg Broodling token with "When this creature dies, create two 1/1 green Infected tokens."

Zerg Evolution - Whenever a creature you control dies, you may pay {b}. If you do, create a 1/1 black Zerg token.