Bloody Mary

{r},{t}: Surveil 2, then you may reveal the top card
of your library. If you do, target creature you
don't control gains -X/-0, where X is the revealed card's mana value.
{x}{r}: Name a card with mana value X or less,
then mill a card. If the milled card is the named card, prevent the next X damage dealt to you, and deal X damage to up to one target creature.