Gateway of Legends

At the beginning of your upkeep, exile the top
card of your library. Then, you may send cards
you own in exile that collectively have the same
mana cost, or more as an empyrean you own
outside of the game. Then sacrifice Gateway of Legends, and put that empyrean from outside of
the game into play. (For example, if you have an Empyrean with a mana cost of {2}{r}{w}, you must
send cards that collectively have at least one red
mana, one white mana, and at least two more mana
of any color i