Playful Kitten

As long as two or more creatures are attacking you, Playful Kitten has "{w}, {t}: Mature this creature." Activate this ability only before blockers are declared. (To mature Playful Kitten, exile it. If you do, search your library for a
non-Young creature card that shares a creature type with it. You may cast it by paying the difference in mana costs between it and this creature. Then shuffle your library.)
They mature rapidly in defense of their kind.