One of the best aspects of Bambi II is evolving Disney's icon of cutesiness into a resourceful guardian for his herd, taking out an entire pack of hunting dogs by himself (bar one which is disposed of by the equally-adorable Thumper and Flower).
Stitch from Lilo & Stitch. He looks like an adorable blue koala with big eyes and can act as such, but he's also the 626th experiment created by an evil scientist with the primary function of destruction, and that trait will show if he feels the need, such as messing with his 'ohana. Many of his experiment "cousins" also count, each with their unique adorable looks and incredible powers.
In Frozen we have Anna and Elsa. Let's see - Cute? Check. Adorable? Check. Able to hold their own in a fight? Double Check.
The Incredibles: Jack-Jack is a baby who can't even talk yet, but both Syndrome and the babysitter learn the kid won the Superpower Lottery, multiple times, with enough powers for a team in his own right.
Jack Skellington and Sally from The Nightmare Before Christmas. The former is one of the most adorable skeletons ever. He also is the scariest guy in town, and if you try to turn his friends into snake-and-spider stew, he will fuck you up. The latter is a sweetheart and also had the guts to go into Oogie Boogie's lair by herself to save Santa.
In the Shrek movies Puss-in-Boots takes serious advantage of this, weaponizing Puppy-Dog Eyes to catch opponents off guard.
The spinoff Puss in Boots introduces another Badass Adorable cat character by the name of Kitty Softpaws, who is skilled and tough on a level fit to rival Puss himself. And a literal "cat burglar."
Rapunzel of Tangled was fully capable of bringing down any of the thugs in the Snuggly Duckling with her all-purpose whip (i.e. her hair) and Frying Pan of Doom but she didn't have to. They were already subdued by her pretty, endearing, 'I have a dream' adorableness.
Morph on Treasure Planet. Seems like a cute, little blob reminiscent of Ditto, right? Not only is he capable of transforming into any given person or object (still remains the same size when in normal form), but can utter very snarky phrases like a parrot, and, when against Ax-Crazy Scroop, is able to put up a decent fight for several minutes. Badass Adorable, indeed.
Margo, Edith, and Agnes from Despicable Me. Three absolutely adorable and adopted girls who are also intelligent and ACT tough as hell. Gru, the minions, and Lucy also apply, but for Lucy in a Adorkable way.
Uni-Kitty from The LEGO Movie is, as her name implies, a half-kitten, half-unicorn. She's pink and has a very sweet personality. If provoked far enough, however, she is capable of effortlessly defeating micromanagers unarmed, the only character to demonstrate this trait.
Baymax from Big Hero 6 is a gentle, inflatable robotic nurse whose entire purpose is to be huggable and nonthreatening, and who routinely dispenses hugs and lollipops as treatment. He very closely resembles a walking marshmallow. However, he's capable of lifting 1000 pounds, and when Hiro upgrades him with armor and a chip that gives him combat capabilities, he becomes the powerhouse of the group. His adorable personality persists, even while punching through concrete, until Hiro takes out his healthcare chip against Baymax's will, at which point he becomes deadly.
Hiro also counts; Along with his goofy gap-toothed smile, it helps that he is not only the leader, but also the youngest and smallest of the team. He is also the team member whose tech suit doesn't have any abilities.
Honey Lemon is a nerdy, dorky Genki Girl who's as sweet as her namesake and has a wardrobe straight out of a 60's fashion magazine. She can do beaucoup damage when given a miniature chemistry lab (that looks like a pink purse with a heart-shaped display screen), and she's brave enough to face berserk!Baymax alone, with no chemical capsules ready, long enough to reinsert his healthcare chip.
Judy Hopps from Zootopia. As a bunny she's got adorable covered and during her Training Montage at the police academy it is shown that she developed the agility and skill to take down a rhino in the boxing ring. Her strength is also impressive as she is shown clinging to the Sky Tram platform with one paw and able to hold onto Nick's paw while swinging on a vine despite his larger size.
The Equestria Girls movies essentially translate the Badass Adorable tendencies of MLP:FIM characters into their human counterparts, leading to moments like the motocross pictured above.