"You're pathetic. One of the best minds on the planet and you waste it for years, doing magic tricks — then trying to best a man who'd never really harm you, despite your endless provocation. But that's the difference between my husband and me. He doesn't understand revenge. Me? I can't decide which of the many ways I can hurt you I'm going to use."
In the same vein, you also have Gosalyn and Launchpad. At the end of the first storyline, Gosalyn has control of the Gizmoduck suit, becoming Gosmoduck, and Launchpad is given Quackwerks by Scrooge McDuck, giving him a literal army of robots at his disposal.
The 1st volume of French comic Dungeon revolves around initially helpless and cowardly lead character Herbert the duck Taking a Level in Badass over and over again. By the end, he has a magic sword he's one Great Deed away from being able to wield, that, if touched by another, will turn him into one of its previous bearers to defend itself — unfortunately, not all of them are awesome, and it can be exploited by forcing him to cycle through forms too quickly to actually react — can't be killed by normal means because his heart was first removed, then eaten by a Bewmew — granting it a soul, and the now-sapient... blob-thingy now acts as his loyal servant and bodyguard in thanks — and is a master of the stick and the feather — since he's a duck and covered with feathers, this means he can dismember and eviscerate opponents completely unarmed.
In the first issue of G.I. Joe: Cobra, we watch Chuckles gain Badass XP in a training sequence with Jinx.
Chuckles has always been badass in the comics. He has consistently been shown as a competent combatant, and as a veteran undercover agent he's one of the most skilled intelligence analysts and operation planners in G.I. Joe. On top of that is the undercover work itself, where his Nerves of Steel show best. The problem is that most people take one look at him, and decide he's a joke based purely on appearance.
In The Incredibles, Xander goes from a regular teenager to a self-made super that can keep up with Violet.
In Volume 1, Kick-Ass was absolutely pathetic in a fight. In Volume 2, he receives Training from Hell from Hit-Girl and learns how to actually fight. Heck, during his team-up with Doctor Gravity, he effortlessly beats the tar out of two hoods (something he couldn't do in the first issue of the series), and this is before Hit-Girl's training! In Volume 3, he holds his own against six thugs, two of whom were holding guns to his head at the start. Though he eventually loses, he points out his one mistake immediately after the fact, implying that he was capable of taking them on a good day.
Scrooge McDuck doesn't just gain one level during the course of his life in The Life and Times of Scrooge McDuck — he gains twelve. In fact, he gets so badass that people all over the globe have heard of him and his exploits; in fact, he scares away Wyatt Earp, the legendary gunslinger, by simply standing beside him. Every Chapter has a third part in which the raw badassery of Scrooge shows just how he defeated his adversaries and became the richest duck in the world, including destroying an entire steamboat alone, unarmed, and while chained down. Never mock Scrooge's family.
Issue #2 is the first time that the audience gets to see the changelings use something besides direct combat. They are much more dangerous outside of a melee, using indirect attacks to divide their enemies and turn them against each other, without them even realizing that the changelings are attacking them.
At the beginning of the Paperinik New Adventures series, Paperinik finds that his usual kit of goofy weapons and tools are largely useless against an invading armada of inter-stellar aliens. When he stumbles on the 151st floor of Ducklair Tower, he finds that the resident AI, One, is more than willing to supply him with the necessary weapons and gear necessary to combat not only aliens, but also rogue time-travelers, high-level space-time anomalies, malevolent AIs, suicide terrorists... in short, his competence level goes up significantly.
Lawrence Dobson from Firefly received a Level of Badass in the Serenity comic books.
There were signs of Antoine's improvement were as early as Issue 23, which both had the first hints at romance between him and Bunnie, and Antoine both showing bravery and generally behaving a lot better. His capability in combat was already starting to be established by this time, as in the very next number, not only does he fight as well as Patch/Evil Antoine, who didn't have the cowardly personality, he also easily dispatches Boomer/Evil Rotor.
Sonic: Remember your old yellow streak? Antoine: Oui. I recall it all too well. Sonic: Because I totally could bring it up right now. Antoine: I know. Sonic: I've got a list. Antoine: Stop eet.
Evil Sonic, Sonic's Evil Twin (duh), is nothing more than a minor pest, at best. He spends his time either playing underling for more powerful villains, or behaving like a glorified thug. However, when the new writer comes into the comic, Evil Sonic gets jacked up on chaos energy, gets a makeover, changes his name to "Scourge", and proceeds to kick his threat level up a notch. It doesn't stop there, however — after a few "inspiring" words from Sonic, he returns to his home dimension, applies himself, and conquers his own version of "Moebius" in a matter of DAYS.
Amy Rose went from a young, innocent Damsel in Distress in the Sonic CD issue to a mallet-swinging force to be reckoned with by the Sonic Adventure arc (which went hand-in-hand with similar development in the game itself). While she was previously repeatedly rejected a Freedom Fighter status, she eventually proved herself after single-handedly turning the tide in a handful of battles and is now essentially in the same capability tier as Sonic, Tails, and Knuckles.
Thanks to the Super Genesis Wave from Sonic the Hedgehog/Mega Man: Worlds Collide, all the Freedom Fighters have taken levels of badass. Sonic has obtained his grinding skills and his Homing Attack, him and Tails can perform the tag-team Spin Attack from Sonic the Hedgehog 4 Episode II, Rotor's now a Genius Bruiser, capable of flinging Badniks with ease,, Antoine can now Spin Attack. With his sword and Sally has energy blades on her gloves. Bunnie? Well, she got back her mechanical limbs, something she lost prior. Even Big the Cat has gotten a real boost up, not only getting a Spin Attack of his own, but also being declared the strongest character in the series, stopping Silver Sonic in Spin Attack mode with his bare hands and tossing him away and lifting a car and tossing it away as if you were just tossing a chair pillow to the side.
Several characters gradually become stronger over the events of Fleetway's Sonic the Comic. Amy is the most obvious example, with her transition from girly Damsel in Distress to a crack shotAdaptational Badass and second in command of the Freedom Fighters. Tails also undergoes development from whiny coward to active contributing member to the Freedom Fighters' efforts as well, most notably after Sonic gets stranded in the Special Zone. Additionally, Johnny Lightfoot and Porker Lewis start out as regular Mobian critters that are just there to be captured by Robotnik's forces, but formally join the team later in an active capacity.
Shockwave, once a good-hearted but weak senator becomes one almost tragically when he is disfigured and his mind warped to become devoid of emotions, becoming the ruthlessly deadly cyclops we know and love.
Devastator combines this with Adaptational Badass. His debut in The Transformers: All Hail Megatron established him as powerful, but Omega Supreme took him down easily. After the Constructicons get an upgrade and Prowl is brought in to forcibly replace the deceased Scrapper Devastator is even more powerful than ever defeating Superion and going toe-to-toe with Monstructor who's own debut had him tear Omega apart.
Superion even takes one in The Transformers: Combiner Wars. Whilst he was originally made by Megatron's hasty combiner experiments, and was powerful, but none too smart. Though he put up a good fight, Devastator wasted him. However, after extensive repairs by Wheeljack and the Enigma of Combination (as well as Alpha Bravo brought on to replace a severely damaged member and Powerglide joining the team to serve as a weapon), Superion returns to form. He's smarter and better armored, with his debut fight against Menasor ending in a smash victory.
In Violine, an early villain, Muller, falls to his apparent death in a crocodile filled death trap, loses both arms while fighting them off, and becomes the series' bigger bad after taking a level, becoming a near unstoppable menace.