Chimera Cub

At the beginning of each upkeep put an age
counter on Chimera Cub. Then, if Chimera
Cub has three or more age counters on it, mature it. (To mature Chimera Cub, 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.)
Three adorable heads. Must be akin to triplets. Hopefully each grows at the same rate!