"Eternal Masters", +search, +library, +"onto the battlefield", +!transfigure (2)
Search your library for a green creature card with mana value X or less, put it onto the battlefield, then shuffle. Shuffle Green Sun's Zenith into its owner's library.
As an additional cost to cast this spell, sacrifice a green creature.
Search your library for a green creature card, put it onto the battlefield, then shuffle.
Gatherer works better in the Companion app!