The New FFIV

I have an interesting, yet TERRIBLE, work-around idea for your Twin Magic command.

You could simulate lost MP cost by adding a short reaction command to ALL monsters in the game.

Something like, "If Spell [Comet] used, target Character ID [Porom,Palom], use [Osmose]"

And then make an Osmose spell with no animation that will always hit Palom and Porom.

You could make more interesting scripts for monsters too, so that all monsters react differently to Twin spells. And make -that- their gimmick, since I'm pretty stumped as to how to make Twin magic work as an actual dual-tech that requires both of them to even be in the same party. (Apart from making Twin magic depend on monster AI as well. Such as, making Porom/Palom's command effectively do nothing, but once cast, it would activate a line of AI code for each monster that says "If [CometA] cast, and If PCIDs [Palom,Porom] are both present, then Cast [CometB] on Monster party")

Weird, and it uses a lot of AI code space, but certainly doable!

And you wouldn't have to/want to write it on EVERY enemy, just on enemies that will be in formations by themselves. If you have two enemies with the same AI in battle, then it would likely result in the command getting doubled (though that might be AWESOME and worth the MP cost).

Hmm... actually, this might make for an interesting way to do dual-techs, Chrono Trigger style.