Steven, K Y & S

Menace, deathtouch, first strike
When, Steven, K Y & S enters the battlefield,
each player mills 10 cards.
Whenever Steven, K Y & S attacks, you may cast target non-permanent spell from your graveyard,
it costs X less where X is the number of creatures
in your graveyard.
Whenever you cast a spell from your graveyard,
if it has X in its cost, double the value of X.