Massacre Twins

Menace, deathtouch
When Massacre Twins enters the battlefield, all
other creatures get -1/-1 until end of turn and you create a black 2/2 Zombie Knight creature token.
Whenever another creature dies this turn, all other creatures get -1/-1 until end of turn. At the
beginning of the next end step, create X black 2/2 Zombie Knight creature tokens, where X is the
number of creatures that died this turn.