Obus, Devil pact signatory

Whenever you sacrifice a creature, you may
untap Obus.
{x},{t}: Reveal cards from the top of your
library until you reveal a creature card with
converted mana cost equal or less than X. When
you do, you may put it on the battlefield without
paying it's mana cost. Then, shuffle your library
Sacrifice a creature: Take damage equal to the
number of creatures under your control