I'm stuck in the battle with the demon General Greed.. When I'm about to finish it it keeps regenerating it's health.. Also I'm stuck in lvl1 Celestian form.. How do I level up? Is Celica's max lvl 95??
This is an RPG, so learn to develop your character's skills. All the basic information about the game mechanics is available in the Agranor Library, especially the book on skills.
For example, in your case, Celica should already be able to drain magic power from her opponents without needing to use artifacts in her small inventory.
So, help Celica become an excellent mage, and your current character level will be sufficient.
It might be late but, greed is a major pain he heals multiple times but, after few heals he stops healing. When I fought him I thought I had to either lose or something but no you just have to defeat him. First try btw(after understanding his mechanics or whatever it wasn't hard). It's a good idea to have light potion/vial to restore celestial power/energy as well as hp and mp.