YOU WILL BOW TO ME.
@Silent_Witness
It’s…complicated. Rather than play a certain number of matches, one will show up each time you start a match and either finish or quit it, including Spirit Board battles or whenever you exit “World of Light”. However, whether you defeat it or not, you have to wait 10 minutes for another to be triggered, though this can be bypassed by quitting and starting the game again.
Any fighters you don’t defeat will wait in “Challenger’s Approach” in Games & More after a set time is done.
Also, there’s a predetermined list of when they’ll show up.
Again, it’s really complicated to explain how and when to get the one you want to appear. Personally, I’d rather just unlock everyone in “World of Light” since I have Spirits and Adventure Skills to make the fights easier.