I don't think any character who is, or could feasibly be, in Smash, MVS, or NASB is a "joke character", and games of that type nigh-inherently cannot have "joke characters". Might be a difference in vocab, but in my mind a "joke character" is a character that, fundamentally, does not fit in and breaks the reality of the game - like Mokap or Gon, both of these contrast the consistent worlds they're in, Mokap being a giant meta joke in a world without many modern elements, while Gon is a cartoonish dinosaur in a relatively realistic world, at least stylistically.
Crossovers as wide-reaching and stylistically diverse as Smash have no consistent style or reality, no immersion to break, putting Mr. G&W or Steve next to Marth is no weirder than putting Mario next to Marth, the only real differences between these two juxtapositions is that you don't see aesthetics like G&W or Steve in external media as much as the big-nosed Franco-Belgian design tropes Mario takes from. This isn't Jump Forces where each series shares many tropes.
The only two other reasons I can see for a character being a "joke" are A. a percieved lack of importance in their source material or overall - something that is an external factor, and not reflected in the game itself in a vacuum (let's say you've lived under a rock for a decade and have never heard of Adventure Time, how are you supposed to know Banana Guard is just a bit player, let alone funny beyond just "bananas are funny"? There's nothing telling you this character is an exception in any way, and therefore nothing to find funny outside of the character's own moveset and personality.) and B. just being a funny character - in which case, where do you draw the line? Where does Crash Bandicoot - the Taz-inspired gibberish-spouting marsupial known for his silly death animations and crotch-chop dance who is widely accepted to not be a joke pick - split away from something like Big the Cat or Rabbids? How is Hugh Neutron "exceptionally jokey" when you've got a game where the most serious, dramatic franchise featured is the show with "My cabbages! my precious cabbages!" as a running gag?