So... Who do you want to see in a Free-For-Battle? This goes for Vanilla NPCs / Creatures and Modded-Lore-Friendly NPCs / Creatures.

I just want an idea on who to spawn in my arena for fun, and all. Already had a Free-For-All battle between some of the toughest enemies I have for my game.

Have you done Dagoth Ur and vivec yet? Or too Cliche?
Also, Guards Vs. anything= instant fun.

I've done Vivec VS Dagoth Ur VS Alex. FFA. Vivec won easily.

I also done a lot of Guards VS (Insert Enemy Here).