You know what I mean! Those were the exceptions, not the norm. To be fair though, the final battle had one major boss from each company, even guest Nintendo through Metal Face.
Problem with Zelda is you gotta have Link, and the problem with Link is that he doesn't talk, limiting the potential for interaction. Though there may some hope for BOTW Link who actually has a defined personality to work with, and actual justification for his silence that he can move past.
Funny you mention Pac-Man, because Tarosuke was playable in Namco X Capcom (don't ask why they did what they did with Dig-Dug protagonist), cameos in X Zone 2 despite still being anime cartoony, and his game's retro medley isn't in Ultimate for some reason
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Tiki shows up both times we visit the Awakening-verse, one of these is the opening where she speaks with Valkyrie. Shulk is only mentioned by Fiora.