The Doctor

Changeling, Colorling (The Doctor is all creature types and all colors at all times.
{w} or {u} or {b} or {r} or {g}: Regenerate The Doctor.
Whenever The Doctor becomes regenerated, pay one mana of any color. If you do, search your library for a card with that color, reveal it, and put it into your hand, then shuffle your library. Put a +1/+1 counter on The Doctor, and he becomes that color.