Bifrost, Bridge of the Gods

{t}: Add one mana of any color.
Channel — {3}{w}{u}{b}{r}{g}, Discard Bifrost,
Bridge of the Gods: Look at the top 4 cards of
your library, you may cast 2 god creature cards
among them this turn without paying their mana
cost. This ability costs {1} less to activate for each
legendary creature you control.