Especially apparent after her glorious reappearance in Revelation, where she utterly decimates Tucker and the Reds at the same time without getting hit once or breaking a sweat. A 7-minute beatdown.
F.I.L.S.S.: Agent Tex is a bit of a badass.
Agent Washington became badass around the time he took down a Hornet solo in less than a minute. Nothing he has done since then has changed this, only added to it. Notable points are taking on the Meta with a chain gun and everything he does from episode 15 onward.
Several characters have done this via Took a Level in Badass, including Wyoming (who did this offscreen after the prequels), Sarge, Tucker and pretty much the entire Blood Gulch crew.
Both characters in Draw With Me. The boy tries to break through the unbreakable glass, and succeeds, but he loses his hand as a result. What does the girl do? She cuts her own arm off for him to use to draw!
Mecha Sonic, the Big Bad of Super Mario Bros. Z, definitely qualifies as this, especially in Episode 6 where he singlehandedly gives the Mario crew, the Axem Rangers and the Koopa Bros one of the most epic fights of the series so far.
Captain Basilisx, the first truly original character in the series, who hands Mario his ass in record time. And he does so in a pitch-black armored spiky shell with Wolverine Claws on his hands after petrifying the rest of the team just by looking at them.
Pretty much any main character, hero or antagonist (and even a few mooks) in the Madness Combat series.
The Shadow, a teenager who fights crime on the streets of LA. His natural healing factor allows for such badass stunts as diving through the windshield of an oncoming car, forcing it to crash, and sending himself and the driver 20 feet through the air, and then standing back up to threaten the driver with more grievous bodily harm.
Firestorm, the Brat Pack's Lancer, during a fight with Gauss, one of the <3-Verse's top villains, found his body trapped in an oxygenless environment. He cut himself open, and used the oxygen in his blood to melt through his bindings, before throwing a fireball at Gauss. All to prove he was ten times the hero his dad was. No mean feat, considering his dad was a 'Nam vet, and was a founding member of the <3-Verse's Avengers equivalent. And His alter ego, the Pumpkin King, who teams up with the Shadow on a regular basis.
Oran is the best representative from Broken Saints for this bill, although Kamimura has his moments.
Zeke Strahm of The Slender Man Mythos. He's one of the few characters who decides to face Slender Man with human awareness; his first reaction is to get a handgun and start shooting at him, even if he's ineffectual. He later decides to find the facts on Slendy, and work out a weakness.
Marble Hornets gives us Jay, who in entry #52 flying tackles and then fights with The Operator. Yes, Jay gets his ass kicked, and he has a killer case of amnesia afterwards, but he's the only one who's been willing to go mano a mano with everyones favorite Eldritch Abomination.
Noah has a rather epic moment when Slendy appears in his hallway. Rather than run, he pulls out a gun, calls him "Buddy" and pops off four shots before Slendy goes One-Winged Angel and forces Noah to retreat.
GASP! The Chief?! I heard that guy drinks tiger blood milkshakes for breakfast and can only orgasm when he wins at Russian Roulette! (The bullets bounce off of his head.)
Sarge counts his pushups using the names of dictators he's defeated, smokes cigars made of the rolled up constitutions of nations he's overthrown, and will pluck eyeballs out places you didn't even know you saw out of.
Squidington, the squid that lives in Gamechap's pond outside his house, is completely invincible. He not only scared a creeper into running away and knocked Gamechap into the air when he fell in the pond, but also survived a Herobrine Biome Buster, something that completely decimated everything within an enormous radius.
He's so badass, that when he was sent in to kill SCP-682, their fight caused the space time continuum to break down.
SCP-1, who is so immensely powerful even the afformentioned 076-2 refuses to fight him!
Worm has quite a few, but the most badass of them is probably Glaistig Uaine. In her backstory alone, she singlehandedly wiped out entire teams of capes sent to apprehend her, and killed the original Gray Boy, one of the most terrifying villains in the world. When we actually get to see her in action, she does not disappoint, managing to actually hinder Scion in direct combat more than the rest of the cast combined.