Gilgamesh
I am summoned.
If Gilgamesh fought seriously, he'd be near-unbeatable in equal terms of engagement. Archer and Shirou could try all they want, but defeating him by themselves would be impossible.
The thing is just that Gilgamesh seldom fights seriously. And he underestimates his opponents. Not to mention having bouts of arrogance that make him do stupid things.
Yeah, this is what will "keep him in check", so to speak. This
is going to be fully incarnated Gil, tho'. I won't lie about that.
Somehting that interests me about playing as Gilgamesh is the clash of ideologies that occur. Gil's path and Karna's path are very different, so I'd like to see them argue, or something along those lines. Stuff like that. The combat and other skills are a pretty great bonus.