OK, here's my idea: I was just thinking about how the name, the "Frozen Flame." Cold + Fire... Hmm... It made me think of Marle and Lucca. Their Antipode attacks are made of cold and fire...and they do Shadow damage. The Frozen Flame is perhaps the strongest "Shadow" oriented thing in existence...
Which brings me to the idea itself. Crono having to fight against Marle and Lucca. It could be done in several ways:
1) They may learn about the above principle I just explained and they may train for the battle with the FF by fighting against each other.
2) They may NOT learn about the above principle, and the FF could possess Marle and Lucca to do its dirty work.
The second method brings in some interesting battle dynamics. Not only would these two at full power kick Crono's butt in the blink of an eye, but it also brings up what I like to think of as the "Rayearth Principle." Magic Knight Rayearth on SNES had several battles like this, where your objective wasn't just "defeat the enemy." Your party members would be turned against you probably 3 or 4 times during the game, and the solution was never to beat them into submission... In some cases, if you beat them, you'd kill them...and that gave you an instant Game Over. In others, you had to hit them once or twice to just make them snap out of it. Or in some cases, if they beat you, you die...Game Over. While in yet others, you had to let them take you out. Still others left no such solution and your only choice was to run away or cast a certain spell on them or whatever, which would heal them mentally and end the battle.
This kind of a concept rarely makes it into American RPGs from what I've seen, so it would strike a lot of players as VERY original if we pulled this in conjunction with that Frozen Flame deal. What do y'all think of this?