As for spells to flash in, you can do so much with a surprise Narset, Parter of Veils in response to a Brainstorm, an unexpected Elesh Norn, Grand Cenobite when an opponent swings out at you, or a sudden The One Ring when somebody tries to take you out
The catch here is that you can just float a ton of mana, resolve Upheaval, then use what mana you have left to deploy mana rocks and threats
The damaged creature will be exiled if it would die for any reason that turn, not just if it dies due to damage from Incendiary Flow
If youre happy smashing your opponents face with whichever creatures RNGesus dealt you, then this could be the game for you
Another angle is to play with some of those suspend cards with no mana cost, like Ancestral Vision, Crashing Footfalls, Resurgent Belief, Lotus Bloom, or Mox Tantalite, and get a zero-mana creature in the graveyard for Ellie and Alan to discover them with