Grigori is such a unique villain because he’s only a villain in the most technical sense. This guy is Neutral at best Neutral Evil at worst because (MEGA SPOILERS)
his whole thing is is finding a worthy protector of the world. The Seneschal is a Pseudo-God that watches over reality from the heights of the Rift but it’s a job that no one can endure forever so they seek out a replacement. The Seneschal is an Arisen that’s defeated the Dragon and defeated the last Seneschal. The Dragon is an Arisen that failed that final test. Grigori calls it The Eternal Ring because this has been a cycle that has gone on forever and will continue forever. It is a duty born in strife because only the strongest and most noble are worthy of the position.
Grigori attacks the world, devastates countries and civilizations looking for those who would challenge him and if he decides they’re worthy to slay him he will turn them into an Arisen. In the first game theirs a doomsday cult that worships him and wants to gain his favor to conquer the world and Grigori decimates them once they reach the foot of his lair. Saying how he doesn’t care about what they want, their ramblings were nonsense and not worth listening to. He doesn’t want to rule the world or destroy it, he doesn’t care about power like that.
The. During the final fight itself where most villains would monologue about how they stand no chance against him, they’ll destroy everything you love, how dare you stand against me?! That sort of stuff but not Grigori. He’s cheering you on. Encouraging you to strike him down and take back your heart, prove to him you’re worthy of it. His dialogue in the first game just before the final fight is him talking highly of mankind.
The monsters of this world are easy to understand. They eat when they’re hungry and sleep when tired of eating, they kill things when they want things to die and nothing more. However this is not mankind, they stand against nature as one, build towards a shared future and create new wonders that allow new life in turn. Mankind has done all this and more. For a champion who would stand against the coming darkness they have to be the greatest of mankind and so the only path is forward.
Not the typical villainous monologue. He deeply admires humanity, and their strength of will. He admires the Arisen most of all because they are the greatest among mortals not for power alone but because of their courage and willpower. If his death will lead to a Guardian over their reality and an inheritor to that cosmic throne then all of this will be worth it.
He’s the new kind of complex Villain because he doesn’t have a real sympathetic backstory. Sure he’s a failed hero from his own time forced to play a villainous role but it’s a role to find a man who can do what he failed to do. He’s a villain only because of the role he plays but not in mind or spirit. To protect the world he must find a worthy heir to take the mantle as protector