The ferocious climax of the Goofy cartoon "Hockey Homicide", which throws in rapid-fire images from past Disney cartoons (many of them sports-themed), including a brief appearance by Monstro the whale from Pinocchio!
The Running Gag involving Icebox Bertino and Fearless Ferguson, the star players of their respective teams that continually get into a fight (strangling one another and beating one another with their hockey sticks), getting sent to the penalty box, then getting right back into a fight once they are released.
Sportscaster: Here come Bertino and Ferguson out of the penalty box... (fight commences between them; referee blows whistle and sends them back into penalty box) Sportscaster: ...and there go Bertino and Ferguson back into the penalty box.
The priceless expression on the general's face when he shakes his head no after Pete asks him if he has seen "a little guy [Donald] that you can't see".
At the very end, Pete is in a cell, wearing a straitjacket, with the now-visible Donald guarding him!
Pete: I ain't crazy! You know I ain't crazy! Go tell the general that I ain't crazy. Donald: Do you think I'm crazy?
In "Pluto's Party", Pluto opens the gate only to be trampled on my a horde of mice children who knock the front gate down. When the leave near the end, the gate stands back up on its own.
Nearly all of Goofy Gymnastics.
In The Plowboy, we see a pig, chicken and goat running Horace and the runaway plow from as they crash into a tree and get combined into some weird hybrid creature.
A lot of moments in Get a Horse!, but special mention goes to the scene where a CGI Horace walks up on the stage wearing modern t-shirt (themed to Marvel, which Disney had only recently bought!) while eating popcorn.
Also Mickey finding a smartphone Horace took, with a guy on the other end shouting "Give me back my phone!".
In Hawaiian Holiday, when Goofy finally succeeds in surfing a recalcitrant wave, after he shouts triumphantly, "Hey, look! I made it!", a voice is heard saying, "Oh yeah?", before the wave throws Goofy off again. It's possible that it was the wave itself that said this line.
Pete's unintelligible babbling as he announces the train stops in Mr. Mouse Takes a Trip.
The flypaper sequence in Playful Pluto. There's a reason it was used on Sullivan's Travels to show the power of laughter.