Rakdos, the Muscle

Flying, trample
Whenever you sacrifice another creature, exile
cards equal to its mana value from the top of
target player's library. Until your next end step,
you may play those cards, and mana of any type
can be spent to cast those spells.
Sacrifice another creature: Rakdos, the Muscle
gains indestructible until end of turn. Tap it.
Activate only once each turn.