Yoriel, Gatherer of Giants

{t}: Add {g} or {u} to your mana pool for each
creature with power 4 or greater you control.
Whenever you tap Yoriel for mana, you may
search your library for a creature card with
converted mana cost equal or less to the amount
of mana Yoriel generated this turn and put it on
the top of your library.
Tap a creature with power 4 or greater:
Draw a card.