I rediscovered the moment in episode 20 when Lelouch and Suzaku team up to take down the Chinese Federation base, and thought it'd be great to capture that on a card. There are a couple of great shots of the Gawain IFX-V301 and the Lancelot Z-01 zooming together through twin holes in the wall that'd make nice art for this card. Amusingly, the name Unlikely Alliance is taken by a bad old card so I need to use a synonym here.

Mechanically, this is a take on green's recent mechanic of one-sided fight, as in Monstrous Onslaught, Nature's Way, Clear Shot, Moonlight Hunt, Rabid Bite and Nissa's Judgment. It has the interesting aspect that the damage-dealing creatures don't both have to be yours, which was fairly important to the flavour. In fact, as currently worded none of them have to be yours, if the opponent's creature base is sufficiently diverse in colours. That's a bit of a bend of green's colour pie; it'd be better in red from that POV, but this set is going to be short of things for green to do and so I'd like to keep this green if I can.

It gets away with being cheaper than Blood Feud because it's only ever going to kill one creature.

Huh. Yes, very nice idea. I like the name, I think "team-up" works better than alliance.

I am also worried a bit about grokking the card and about it potentially being too good creature kill, but the hurdle of having three different colour creatures at all is sufficiently large it's actually hard to use at all. Even if you have a deck full of artifact creatures.

Who chooses which creatures deal the damage?

The caster of the spell. It's meant to be that at casting time, when choosing targets you also choose which two will be dealing damage and which will be receiving it. I brainstormed a few wordings but they were all a bit tricky to combine with the "no colour shared among any two of the three" condition.

Mmmm.

Choose two target creatures that don't share a colour; they deal damage equal to their power to a third target creature that doesn't share a colour with either of them.

Yeah; I prefer your wording and the fairly obvious rule "My spell, my choice".

Although; if you reallllly want to keep flavour; the controller of each creature chooses which other creature to deal the damage to simultaneously; and they only actually deal it if to a clear majority target... Which is now, amusingly, less good at dealing direct damage; but more red :)