Sphinx of the Second Sun
An extra untap, upkeep, and draw step, folded in after your postcombat main phase: that is the entire mechanism, and blue has rarely opened a door this strange. The additional beginning phase does not hand you another combat or main phase, so the naive read (a second turn) is wrong. The turn moves straight from that phase to the ending phase, which means the untapped lands it produces can only fuel instants and activated abilities, not another round of sorcery-speed plays. What it reliably gives is one more draw before the turn ends. That is the floor. The ceiling lives in every trigger keyed to your upkeep or to untapping: any permanent that pays out during that step now pays out twice a turn, and any effect that snowballs off untapped mana gets a second bite. The design cost is bluntly stated in the mana value and the body: at eight mana, this 6/6 flier lands with no swing in it and cannot enter the red zone until a later turn. But it does not sit idle. Cast it precombat and it is already on the field when the postcombat main begins, so it fires that same turn to untap your lands and draw. What it asks of a deck is upkeep triggers stacked behind it, and what it pays is permission to run engines built around a single activation per turn, on the promise of firing them twice.
