Rey Mysterio, a semi-civilian Non-Action Guy wrestler, engages an Elite in close combat and actually holds his own.
Blink, an excitable teen girl Original Character, can teleport effortlessly, but she can rarely bring along even one other person without mishap. During this challenge, she teleports an entire Phantom dropship. Granted, she's tired, disoriented, and sick afterward, but still...
Jorge responding to Tron's stubborn disregard for civilians and the rest of Noble Team (Tron stating that it would be best to leave them to die and finish the challenge quickly) by throwing Tron out of a moving aircraft.
Eddie, in demon mode, leaping out of his transport to go one-on-one against a Covenant ship.
Gordon pushing himself to get through a hallway filled with microwaves to disable the Combine's reactor.
Samurai Jack, doing what he does best, even as he's being steadily overwhelmed by Combine synths.
Immediately followed by Jack and Kimimaro being Back-to-Back Badasses, fighting their way down through the advancing horde and regrouping with the others.
After the Half-Life challenge, Subaru's efforts to create an adaptable training robot capable of utilizing weapons and abilities from different universes goes disastrously wrong; it runs amok and begins imitating the Champions, past and present, attacking everybody at once in numerous waves, greater numbers and greater intensities. After several rounds, this finally culminates in a boss round against nothing less than an imitation of Megatron. Naturally, this pisses Ravage off like you would not believe, and he winds up summoning a Megatron of his own to duke it out with the renegade training robot. Even when it knocks Ravage into a wall and shapeshifts into the more powerful Galvatron, it proves no match, and Megatron proceeds to utterly wreck its shit in short order; before destroying the hapless imposter, Megs gives his imposter a nifty little monologue:
"You attacked one of my subordinates. You stole my face like a human pickpocket might steal those worthless scraps of pressed plant matter they use as currency, and then discarded it like chaff when it no longer suited your purpose, like an organic throwing away an expendable pair of pants. Worst of all, you dared to pass yourself off as a Decepticon, and could not even hold your own against a real Decepticon to back up that false claim. I do not know what manner of pathetic shapeshifter you are, coward, but the universe shall be infinitely better without your weakling, mongrel chassis in it."
And then, when he administers the killing blow to his impersonator, it proves too much for the berserk training program and causes it to crash in the most spectacular manner possible. He may have only appeared for a single page, but damn if Megatron wasn't awesome.
Blink has often bragged of her skill in being able to steal anything. This is proven beyond a shadow of a doubt when it is revealed she is in possession of The Shot Heard Around the Universe.
During the Crossover Challenge, Link taking down an enemy gunship in a manner most stylish and awesome, and then later on regaining control of his body from Dark Link through sheer force of will.
Later in the Crossover Challenge, Samurai Jack, Kimimaro, Gordon, Spriggan, Icarax, the Doctor and Link all defend Doctor Langely in a battle with her inner demons, cutting them down in swathes, all the while shouting encouragements - then she breaks free of them with the help of several of the Champions, tearing her flesh to shreds in the process, while grinding out this speech: "I do know who I am - I am Aska Langley-Ikari, the one and only! I! Am! Me!!!" Awesome.
At the tail end of Season 1, Gordon Freeman gets to go home. One problem: The G-Man. After G-Man implies he's about to place Gordon back in stasis, Gordon pulls out his gun... and jams the barrel in G-Man's mouth and fires, killing the Humanoid Abomination with The Shot Heard Round The Universe.
Gordon: "Get the fuck out of my life!" (BLAM)
During Phi's flashback, one of the previous champions, a man who had no fighting experience or powers beats up a Nomad with with his bare hands and kills him. Turns out that the Champion was Phi, originally Tomoya, and that the Nomad was the original Phi.
Doesn't quite help that said Nomad was pretty weak and only got weaker when the title changes hands.
Shotaro and Dubix teaming up to from Kamen Rider Joker Double Form, a Spiritual Successor to the original Kamen Rider Double. All while singing a slightly modified version of Beelzeboss.
In the beginning of the Roger Rabbit challenge, Kamina, the chief of the animated division of the LAPD, makes his grand entrance by driving through a wall with his car, punching Spongebob in the air and landing on top of the car... which landed on top of Spongebob... while ablaze.
A Game Of Gods: Taskforce Sifuri
The first battle, which for the first time in a long while, was encouraged by the GM.
It gets more epic once they go into the forest and one of them gets lit on fire along with the rest of the forest. Then when Suzaku succumbs to his Geass command, to quote a certain Big Bad, they were in for a big ol' storm of chaos.