Shivan Shorestalker

When Shivan Shorestalker attacks, reveal cards
from the top of your library until you reveal
an instant or sorcery spell. Exile that card. You
may cast it this turn. Put the rest on the bottom
in a random order.
Whenever you cast an instant or sorcery
spell, Shivan Shorestalker gets +X/+0 until end
of turn, where X is equal to that spell's converted
mana cost.