The Masked One

Whenever another creature you control dies, you
may search your library for a creature card with
converted mana cost equal to it, reveal it, then
put it into your hand. If you do, shuffle your
library.
{2}{u}{b}{g}, Sacrifice a creature: Choose up to one target creature in your graveyard. Return that
creature to the battlefield. It gains haste. Return
it to your hand at the end of your turn.