That's just scratching the surface, and it's worth mentioning that, even if it turns into another creature for the turn, Scion still doles out commander damage
I'd be remiss in talking about Green without mentioning all the Elves cards printed in Foundations
Since all the combos require my commander to instantly win, a quick n' easy way to do this would be just to swap Niv-Mizzet, Parun out with a noncombo commander and call it a day: Niv-Mizzet, Dracogenius is a straightforward swap if you still want to keep The Firemind in your command zone, or you can switch to another Spellslinger commander like Kaza, Roil Chaser
The Legend of Kuruk / Avatar Kuruk The Legend of Kuruk lets you Preordain twice before it becomes a finisher in Avatar Kuruk, which acts like a Young Pyromancer
Tide Shaper Merfolk with a purpose Were getting a few very interesting merfolk in Modern Horizons 2
Funny enough, one of my favorite Standard decks I've ever played was a Delirium deck