Rakdos Keyrune

Artifact

Oracle text:

{T} : Add {B} or {R} .
{B} {R} : Rakdos Keyrune becomes a 3/1 black and red Devil artifact creature with first strike until end of turn.

The Rakdos use it for everything you can think of and plenty more than that.

Collection:

Return to Ravnica

Rarity:

Uncommon