Toph's Taunt has her replicating this scene from Avatar, where she waves her hand, fingers outstretched, multiple times in front of her face to signify that she is blind.
Speaking of Toph, being one of the most awesome characters in the Avatar canon, (she literally invented Metalbending) she gives off some hilariously cheesy lines:
Ready to rock? How's that for rocking the world I am melon lord!
The Ham and Cheese narrator pulls off some funny one-liners like "Major damage!" and "That's gotta hurt!" and his overall Large Ham energy helps make some satisfying moments funny.
Nigel's entire moveset is hilariously silly but special mention goes to his up special where he becomes a whale and crashes down on his foes. It's hard to tell what's funnier, the silly sound he makes, the fact that he can make himself weigh over 2 tons at will, or the funny pose he assumes during the move.
Jellyfish Fields has calm, cheery music peppered with dolphin noises. It seems perfectly innocent...until you remember what SpongeBob SquarePants uses dolphin sounds for, making it sound like somebody is cursing in the background. That being said, the use of dolphin chitters along with the percussion in the song is likely meant to reference the musical number end of the season 1 episode Jellyfish Jam.
In Technodrome Takedown, Krang is watching the fight from his flying suit. Said suit will pull Krang out of it so he can get a better look... then drop him. Oops.
Some of the characters take Sore Loser to its limits. Highlights include SpongeBob and Jenny spewing Ocular Gushers, Garfield throwing a tantrum complete with a text bubble saying "WAAAAAAH!", Cat throttling Dog, and Ren crying his buggy little eyes out as Stimpy tries to comfort his hideous friend-lover-roommate-whatever.
Remember that bit where GIR was way too happy to self-destruct? Well now he can do that multiple times in a battle. You can even make him stop running before he attacks someone, making him go from overly giddy to just standing there, looking lost. What's more, he attacks by clinging onto opponents and exploding, making it the embodiment of this gem.
On the subject of Zim, his stage, Irken Armada, features the Massive in the background. One can imagine what the Tallest must be thinking in there when they look out the window and see Zim himself. Made even funnier by the Massive taking off rather than staying to witness the fight, as if they saw Zim and told the pilots to rush it.
Hugh's up special has him bounce himself into the air while sitting on a banana. Specifically the one he sat on when he was seven years old. Here, it's revealed that the banana is actually an inflated bouncer Hugh is playing on. No wonder why it changed his life!
Remember that scene in The Ren & Stimpy Show where Ren dreams about becoming president and blowing up a chunk of the earth? Well, his and Stimpy's Super Attack brings it back, only this time, he BLOWS THE WHOLE PLANET UP INSTEAD!
Garfield's new neutral special in All Star Brawl 2 brings out his "old-school shine" — as in, he spontaneously turns into his 1978 self, and the move functions basically the same as MeleeFox and Falco's Shinesnote It's active on frame 1, has a short-lasting damaging hitbox on activation and a reflecting hitbox for the remainder of the move, and it can be jump-canceled, enabling the user to do things like shine/wavedash chains. It's the one odd move out in Garfield's revamped moveset, and it's hilarious just for being so absurd even by the fat cat's usual standards.
Characters in 2 have special interactions with the NPCs in the hub as well as bosses in the campaign, and there are some moments worth a chuckle.
When Garfield speaks to Gary, the cat is understandably a bit confused when the snail meows at him.
Pretty much every interaction Garfield has with the various boss characters, as it's clear that Garfield (being Garfield) doesn't care what they have to say and just wants to go home to resume his usual eating and sleeping. Garfield's attitude even frustrates Vlad, when Garfield continues to snark away and express disinterest in what Vlad has to say in the face of all of reality being on the brink of destruction:
Vlad: How can even a cat be bored at a time like this?!
In the campaign, some stages involve fighting waves of random Mooks from various different Nickelodeon universes. Most of them make sense in their universe, such as SpongeBob and friends having to fight jellyfish and Bucket Helmeted citizens, Jenny having to fight Cluster Drones, Danny fighting various ghosts, and El Tigre having to fight off Skeleton Banditos. Then we get to the mooks that represent Garfield's universe, and all of them are Anthropomorphic Food. Guessing Jon forgot to clean out the fridge again if the fat cat has to fight off the food he usually just eats.
Grandma Gertie's Super Attack starts off with her rewiring a cable of some kind, where it follows up by taking a page out of asdfmovie and A TRAIN COMING OUT OF NOWHERE AND RAMMING THE OPPONENT !
Her down special has her pull a random object from her bag, where it's either a flyswatter, a pile of tacks, or a GRAND PIANO.
Heck, the entire FACT that Grandma Gertie, who is mostly a side character in Hey Arnold!, is in a fighting game as the second representative for the show is worth a laugh for how absurd it is.
from Avatar, where she waves her hand, fingers outstretched, multiple times in front of her face to signify that she is blind.