All Main Villain fights in Final Fantasy

All Boss Fights in Nier Gestalt

Not considered as RPG by many but as Adventure, Action-RPG-Adventure in my eyes: Ganon Battles in Zelda

Final Battles in the Kingdom Hearts Saga

Another Action-RPG Adventure: Darksiders. Here the Guardian in Darksiders II

Bumblebee Princess Flameu in Atelier Escha & Logy