Real talk, now that I think about it, Ultima Weapon would be one of the most likely FF bosses... though it would use its FFVII which is meh. Well, after you
I'll do a boss list for some franchise since I'm in the mood for it. All stages are flat like Dracula's and Rathalos's unless specified otherwise, this really is only for the background:
Return of Petey(fought in Delfino Plaza) and King Boo is added(fights with other Boos helping. Tends to become intangible. Fought on Boo Mansion)
Guardian(runs across the stage attacking players with ancient weapons such as the axe, spear and sword, and will occasionally fire off laser that result in a OHKO if hit. Fought on Central Hyrule Field)
Kraid(the largest of all bosses, based on his Super Metroid fight. Fought on Brinstar, only boss with platforms for obvious reasons.)
Return of Rayquaza(fought on Kalos Pokemon League) and Arceus(uses moves of all types and will change colors to warn which moves it's about to unleash. Normal type has it use Judgement which is basically Taboo's OHKO waves. Fought on Spear Pillar.)
Return of Porky(fought on New Pork City)
Grima(the hitbox is a shadowy Robin, however, the head is the one doing the attacking but can't be damaged. It'll constantly try to defend the body and attacks with its breath and the spikes. Fought on Grima's Back)
Turn Metal Face into a full boss(fought on Gaur Plains)
One-Winged Angel Sephiroth(you know the drill. Fought on ??? Space I guess)