Seru Deathsteed

Instinct (When this creature attacks, discard a card
at random. This creature gets +X/+X until end of
turn, where X is the discarded card's converted mana
cost.)
Flying, deathtouch
Whenever you discard a creature card, put X
+1/+1 counters on Seru Deathsteed, where X is
that creatures power.