Anyway, nominations. Or "nomination" because I'll think of others later but damn it I used to try getting this guy into every single contest he was eligible for (and failed every time) and I will keep that tradition alive!
1. Lord Foul (The Chronicles of Thomas Covenant)
Basic summary of his powers is control of various forms of magic (for lack of a better word) with enough raw power at his peak to make someone unable to oppose him without the power needed being enough to risk destroying the planet. Specializes in less direct combat though - he's been known to use illusions, his powers inherently corrupt people into serving his will if people try to manipulate them/use them for themselves, and his much less powerful servants have been shown to use a lot of clever tactics in warfare like animating the dirt in the form of all those who have died in a given area to attack without risking casualties to their own army, although the preparation time on these would mean he'd need to create a lot of distance to make use of them in a one on one match. Additionally, he pretty much automatically enslaves any undead he encounters, and is effectively immune to time manipulation (because screwing with time will "unseal" him from the planet he's on and make him more powerful) and mind control (because it would eventually enslave whoever tried to control him, and he explicitly cannot be defeated by any power that isn't being guided by the free will of its user).
On the other hand, he can be defeated if you can just keep overwhelming him with raw power, by enduring his powers long enough that he drains himself of power, or by some more nebulous means like defeating him then refusing to kill him or if you can give him cause to want to temporarily destroy himself (as in, to leave himself unable to act for centuries) in order to make you die in total despair and then you can actually survive the means used to do it.
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We clasped our hands, our hands in praise of a conquerors right to tyranny