Note: these crossovers are character-specific
Papa Louie and Peppino Spaghetti (Pizza Tower): Imagine what culinary shenanigans they'd get up to!
Prudence and Lacey (Lacey's Games): Prudence would be Lacey's emotional support friend, plus they both have (or in Lacey's case, had) dogs.
Timm and Jimmy T. (WarioWare): They'd be friends for sure after meeting up at the dance studio. They'd probably get drinks afterward.
Quinn and Judgement Boy (Gregory Horror Show): It would be a nightmare having to take Quinn's order AND face one of JB's moral dilemmas.
Boomer and Popee (Popee The Performer): Stunts would go from gnarly as in cool to gnarly as in "OH MY GOSH THEY KILLED KEDAMONO (again)!"
Duke Gotcha and Dora Smarmy (Crashbox): They'd be brawling on the ground to see who covers the next story while the news crews just watch.
Chester and Sam Finch (What Remains Of Edith Finch): If Sam Finch wasn't, you know, dead, they'd probably be good friends.
Iggy and Masada (Yume Nikki): Iggy would be hyped to see an alien, while Masada would just be playing his keyboard without a care.
Mindy and Takoyama (Parappa The Rapper): Mindy would get roughly four times the amount of work done with him as her co-hairdresser.
C.J. Friskins and The Judge/Pablo (OFF): C.J. would be hugging Pablo while he screamed at him for it.
Jojo and Gordon Ramsey: You'd be praying not only to God, but to everyone else if they both showed up at once.