Enchant creature
Enchanted creature gets +2/+1 as long as it's black. Otherwise, it gets -1/-2.
As long as enchanted creature is black, it gets +2/+1; otherwise, it gets -1/-2.
"Phyrexia's touch is painful to all but the blackest of hearts."
—Gerda Äagesdotter, Archmage of the Unseen