...do you actually want me to crack out my favorite very silly subject for this? Because I know shared skeletons and animation sets, you don't wanna fight me on this:
- Omega's a gigantoad, as we all know.
- Althyk is an Odin reskin. (In fact Odin's mostly borrowing from the dullahans.)
- Trinity Seeker, the first Delubrum Reginae Trinity boss, is Ravana. There's a good few Ravana reskins around, actually, it's hard to count 'em up.
- Trinity Avowed, the second Delubrum Reginae Trinity boss (the one with the heat mechanics) is Shiva. This might also be the starting point for Asura, the Fanfest event boss, but we can't be sure yet.
- Hephaistos in P8 incorporates both Byakko and the centaur skeleton that started off as Ultima Weapon.
- Thunder God Cid in Orbonne is reused both for Perfect Thordan in Dragonsong Reprise, and Excalibur in Eureka Orthos.
- Scathach's model is reused for Omega-F, Penthesilea, the Spectral Necromancer, and a good few others; basically any floating female character wielding a long weapon of some kind.
- Inversely, Omega-M was reused for the Warrior of Light trial.
- All the Stormblood Eureka 'zone boss' enemies are reskins: Pazuzu is Diablos, Louhi is Cruise Chaser, and Providence Watcher is Nidhogg.
- Nael Deus Darnus' skeleton has been used in a bunch of places, perhaps most prominent being Nidhogg's Dragoon form in Final Steps.
- Sephirot was reused for Chaos in the Omega raids.
- The Diablo Armament, final boss of the Dalriada, is actually just NeoExDeath.
- If you want to specifically talk trials-to-trials, Ifrit actually was reused: as Diamond Weapon's unarmored form.
Hell, Thordan's skeleton has also been reused a couple times, as Exdeath in the Omega raids and Siegfried in the Masked Carnivale. You just probably didn't notice because you think of Thordan as 'big guy with big sword', so them changing up the weapon in question threw you off; fair enough, it was a surprise when I found out too!