I think Phoenix would be cool, but I’m not quite sure what kind of abilities it would have. Perhaps it could have a big fire attack and the ability to resurrect other Aeons (probably for a high MP cost since that seems rather powerful).
Actually if you check their the names of the GFs, they are Cactuar and Tonberry as GFs.
You have to defeat the BOSSES Jumbo Cactuar and Tonberry King to get them though. And also at the end of the fights they change back into their normal forms anyway.
Knights of the Round would be cool, but I think it would be difficult to fit all 13 on the screen at once, so you’d probably have the main one on, who calls forth the others as needed. That would be cool.
They don’t just shirnk, they also loose a couple of details that made them different. Like Jumbo looses his moustache, and becomes a regular Cactuar. And King looses his crown, and becomes a rgular Tonberry.
So they are not the same one.
Yojimbo confuses me a little because some times the weaker attacks will do more damage. Of course, until I fully charge whoever’s weapon, he’s stuck at 9999 for pretty much all of them.