Swift Demise I count Swift Demise because it would work with many alpha strikes (yours or your opponent's), but more importantly pairs up beautifully with cards that spread one damage to all your opponent's creatures like Iroh's Demonstration and End the Festivities
Spell Mastery isn't any easier to get than delirium and it is a touch narrower too
That being said, you're fairly Commander-reliant, as one might expect of a Voltron strategy, so even though Firion often will have Haste when he hits the board a second time, as soon as you're casting him for 7+ mana, you're having a rough time of itCommand Beacon or even Campfire could be considerations to get Firion back in the game, with special mention of Campfire also shuffling lost Creatures back into the Library for further polymorphs
Emerald Sapphire is all about Inventors, and when characters with that keyword enter the mix youll want to compliment them with Support characters, Locations, and Items that allow you take full advantage
It's also only found on red, white, or blue creatures as it was originally a keyword associated with the Jeskai Way faction in Khans of Takir