Claim of Currents

(You may cast a legendary instant only if you control
a legendary creature or planeswalker.)
Claim of Currents costs {x} less to cast for each
other natural card you've played this turn.
(Lands, tribals, and nonartifact creatures are Natural.)
Return to their owners hands all creatures who
have attacked you or a planeswalker you control
this game.
X is the number of natural Cards in your
graveyard.