While the AT-AT has the size advantage at 74 feet tall as opposed to the Omnidroid's 50 feet, the Omnidroid outclasses the AT-AT in terms of maneuverability, armor, and weaponry. Plus, the Omnidroid's only real weakness is its own weaponry. It took five supers working together to take down the Omnidroid (which was specifically designed to kill supers), while a simple tow cable wrapped around the legs has proven more than enough to neutralize an AT-AT, which was primarily designed to transport troops. In short, the Omnidroid curbstomps. Optimus Prime (Transformers G1) vs. Leader-1 (Challenge of the GoBots). And no, anything to the effect of "OPTIMUS WINS BCUZ GOBOTS SUX LOLOLOLOLOLOL" is not an acceptable answer.
Optimus, not cause Leader One sucks, but because Leader One just isn't bot enough. The Trasformers towered over humans, where Gobots were only maybe twice the humans size. Leader One just has laser hands, and can fly. Optimus has experience fighting fliers and if we're going by his very first form, has his combat deck and Roller to assist him. Not to mention the hand blast aren't really effective against Renegades, Op has fried Decepticon with his gun. Megatron vs Skeletor
Well, since the Balrog is a massive fire beast who kinda killed Gandalf--wait, you meant the Street Fighter character, didn't you? Silly me! Balrog ONCE KILLED AN ELEPHANT WITH ONE PUNCH IN THE FACE. Apollo got killed in a match with Ivan Drago, who is nowhere near that strong. So Apollo is, to put it bluntly, screwed. Papyrus (Undertale) vs. Skeletor (He-Man and the Masters of the Universe).
A fully-leveled Dovahkiin can tank anything Link can throw at him, and can hit like a level boss. It'd be a long fight, but Dovahkiin has the clear advantage. Mister Rogers in a bloodstained sweater vs Thanos.
Moldorm, I don't know who either it so I'm guessing alphabetically. Sherlock Holmes(Elementary) vs Sherlock Holmes (Sherlock)
The Party Dude. Also don't underestimate Squirrelgirl. She's taken down some bigtime heavy hitters. The cast of That 70's show vs the cast of the Big Bang Theory.