The ending of "Bellboy Donald" counts both for Donald Duck and for whoever was in charge of censoring cartoons in 1942.
For detail, Donald had been putting up with Pete's bratty son through the whole cartoon and wants to punish him, despite the manager telling him he'll be fired if he does. What does Donald do? He sacrifices his job to give the brat his just desserts!
Donald: Am I fired?
Manager: Yes, you're fired!
Donald:*smiles evilly* That's all I needed to know!
*goes behind an ornamental shrub and spanks the living daylights out of Junior*
"Sea Scouts" has Donald defeating a shark with one punch.
With a boost of Mickey's potion, Pluto viciously mauls Pete the dogcatcher in "The Worm Turns".
The same honor goes to a fly who beat up a spider.
And to a mouse who beat up a cat.
And to that same cat who beat up Pluto.
Several instances where Mickey goes action hero, like "Shanghaied" and "Two-Gun Mickey".
Minnie in "Pioneer Days". When Mickey is about to be killed by the Indian chief, she escapes her ropes, picks up a piece of hot coal and stuffs it down the chief's pants.
The 36 second-long fight between Mickey and Julius during the climax of "Runaway Brain" . Say what you will about the Nightmare Fuel in that short, but those have got to be the most epic 36 seconds Mickey Mouse has ever had outside of video games and comics.
Get a Horse! for seamlessly having the characters go from tradition black-and-white animation to color CGI and vice versa.
Mickey's method of dispatching Pete definitely counts.
Alpine Climbers had Donald successfully head-butting an adult goat.
Saving Fifi from a set fire in "Society Dog Show".
Rescuing Dinah from a dog pound in "Canine Casanova".
Rescuing her again from drowning in a pool in "Pluto's Heart Throb".
Alerting the town that disowned him of a damn leak by goading them into chasing him was pretty impressive. The true Awesome Moment of "In Dutch" however probably goes to Dinah plugging the leak with her own rear end.
Peg Leg Pete actually defeats Mickey in winning over Minnie's affections in "The Barn Dance", part due to getting to act like a gentleman towards her instead of kidnapping her. Yeah, it's a Tear Jerker for Mickey, but retroactively, Disney's biggest Ineffectual Sympathetic Villain deserved one victory.
In another case of Minnie being fickle, "Puppy Love" has Mickey accidentally offending her after Pluto switches a gift he brought for her. Minnie gives Mickey a mouthful before he can even explain and tells him to get out. Mickey suddenly gains a backbone and angrily tells her he's done with her, slamming the door behind him with such force that everything on the accompanying wall falls off and breaks, dumbfounding Minnie.