The final confrontation between Matthias and Asmodeus is full of awesome. Especially when you hear it on audio with Brian Jacques reading it.
The epic final battle for Redwall Abbey in the same book as well. With Matthias and Cluny going sword to tail all through the abbey, and ending with Matthias dropping the abbey bell to kill the leader being probably the highlight.
Mind you, Matthias' entrance to that battle is awesome enough. "I AM THAT IS!" - talk about dramatic. Gives this troper shivers of excitement every time.
Orlando: "I've known creatures ten times her size without a quarter of her boldness."
Finnbarr Galedeep's Curb-Stomp Battle with Urgan Nagru in The Bellmaker. He does something you'd expect a badger to do: Finnbarr throws his twin swords to the ground and fights off the Foxwolf using nothing but his claws and teeth. At The Climax, he picks up Urgan by his tail and neck and smashes his head into a heavy log, cracking his skull and driving the wolf skull's fangs into Urgan's head. Oh yeah, he did all this after he got slashed in the face and stabbed with a spear.
When Abbey Dibbuns Bagg, Runn, and Grubb singlehandedly stop a searat invasion at night by cutting the vermin grappling ropes with kitchen knives.
Blaggut when he strangled his evil captain after the captain murdered an Abbeydweller, and then returned to Redwall to own up to it, even giving them the permission to kill him if they wanted. (They didn't).
The death of Brigadier Buckworthy Crumshaw. He charged across the Abbey grounds wielding only his cane, with three arrows in his chest and a sliced apart face and he still grabbed Freeta's sword, twisted it around, and rammed it into her throat before dying. How much more awesome can a Taking You with Me get?
Tam manages to deliver some pretty good zingers to Gulo during their Boss Battle near the end of the book.
Gulo the Savage: *shouting various gory threats* I'll eat thy flesh and gorge on thy bones! Your heart is mine!
Rakkety Tam: Yours? You cannot have my heart, 'tis promised to a fair pretty maid!
Felldoh's duel with Badrang. He takes down his enemy in the coolest way possible (while smiling the whole time), then proceeds to beat him senseless, just as Badrang used to beat his slaves. While he does then get killed by Badrang's horde, he still wipes the floor with most of them. Bonus points for taking a javelin to a sword fight.
Felldoh: "You had me beaten when I was little more than an infant! My father was beaten with the rod because he was old and slow! You never made me cry out!"
From Outcast: Sabretache's duel with Captain Zigu. "You have lived the life of a coward, now learn to die like a soldier, sah!"
When Veil Sixclaw finally meets up with his father Swartt, he goes into full-on Deadpan Snarker mode, and it is awesome. He won't stop even when Swartt starts making death threats. And then he dishes out an epic"The Reason You Suck" Speech about how Swartt is a coward who abandoned him, and that he considers him his ultimate enemy.
Skarlath is pretty much made up of awesome moments, especially his Big Damn Heroes moment when he attacks Warpclaw.
Sunflash killing two adders. By himself. With his bare paws. And this was in Part 1 of the book, which was several years before he Took a Level in Badass and became the Badger Lord of Salamandastron.
Minor character Brinty the mouse gets one in High Rhulain. After a gannet is accidentally pushed out of the Abbey and onto the lawn, it tries to go after a pair of Dibbuns. Brinty charges the thing and tackles it, pummeling it while yelling for it to get out of Redwall until he successfully pushes it out beyond the gates and the gannet goes away. Almost immediately turns into a Tear Jerker in a shocking case of Mood Whiplash when the water rat Goldfish Poop Gang leader hops out of the ditch and kills him, though Skipper kills him with a javelin immediately after.
Later in the same book, after witnessing her friend Pandion Piketalon's murder at the hands of Riggu Felis, Tiria Wildlough's immediate reaction is to load a barbed iron star (which had been embedded in Pandion's beak by Felis early in the book) and launch it at Felis. It pierces him through the forehead, killing him instantly. This was the same guy who had Leatho and the otterclans literally on the run at all times.
Okay, so killing Asmodeus was pretty badass, and then there's the Big Damn Heroes moment when Matthias shows up to save the Abbey with Martin's sword and an army of shrews and sparrows, but Matthias' true Crowning Moment comes shortly after that, when he's up in the bell tower during his final battle with Cluny the Scourge. Cluny has a hostage, so Matthias promises on his honor as a warrior that he'll come down from the tower if the hostage is released first. Cluny agrees, and Matthias comes down... after he cuts the rope holding the bell, which falls and crushes Cluny to death. Proving once again that just because you're honorable doesn't mean you have to be an idiot about it.
Cregga Rose Eyes'—and the rest of the Long Patrol's— Big Damn Heroes moment in The Long Patrol.
In Marlfox, Lady Cregga, an old, blind essentially grandmother/nanny figure managed to use a longbow to fire an arrow from the Abbey to kill what was believed to be the leader of the invaders. Again, old and BLIND.
The adder triplets in Triss. Dude, they effectively got a HYDRA into a book with no real magic. Gotta feel for the snakes, though, especially the only female of the three - imagine spending your life literally joined at what passes for your hips to both your brothers...
What really makes them badass is the fact that they're ten times more dangerous than Princess Kurda and her entire army. Who does Princess Kurda and her whole army kill of relative importance? Drufo. Who do the adder triplets kill? Ovus, Bluddbeak, Captain Plugg Firetail, andShogg, who was one of the main protagonists. Talk about Hero Killers.
Constance the Badger using a giant oak dining table as a rat-flattener, then catching another rat in a fishing net and swinging him repeatedly against a stone wall.
The Reveal of Slagar's true identity. He previously appeared in Redwall, but was bitten by Asmodeus. The only other character in the series to survive an adder's bite is Sunflash, a freaking badger. And Sunflash was given immediate treatment by someone who knew an old remedy for snake venom. Slagar passed out, then woke back up and crawled all the way back to his mother's den, then spent an entire winter treating himself to recover fully.