Griever

[Seraphor]

I agree. But if Ultimecia was Rinoa it would make sense for her to summon Squall's spirit animal and that plot point would serve the purpose of making that connection. But I won't open that can of worms here, I don't think Griever being summoned means much lol

He still looks cool though, and I wouldn't mind seeing him as a trial.

The japanese script literally says she reads Squalls mind and thats how she summons Griever, absolutely no need to her to be Rinoa and cause the plot hole of her killing her younger self, while defeating the point of the core themes of the game.