Altar of the Darkest Sun

Path: Sacrifice three creatures. (the other abilities on
this card are not active until the path has been
completed.)
Whenever a creature is sacrificed, gain {b}{b}{b}
Creatures you control get +1/+1 until the end of
the turn whenever a creature is sacrificed.
—
"We offer up this willing body to you, that you might deliver us into salvation"
-Gura, High Priest of the Darkest Sun