Zerinya, Soul Marauder

Zerinya costs {1} less to cast for each creature that
died this turn.
Double strike, deathtouch, provoke, haste
Afflict 4 (Whenever this creature becomes blocked, defending player loses 4 life.)
Whenever a creature dealt damage by Zerinya
this turn dies, put a +1/+1 counter on Zerinya
and draw a card.