Meaning only ONE character is the perfect fit for #69

You're right. Whatever character gets that slot, they'll be a joke forever. Unless… they already are a joke. So we need a character that can handle being the brunt of jokes and associated with memetic sexual status already.

This can only mean one thing.

IT'S TINGLE TIME BABY

Butt of jokes? Check.
Associated with memetic sexual status? Tingle's Balloon Trip of Love is an official Tingle dating sim game. And have you seen that spandex? CHECK.
Not currently deconfirmed by the game? His assist trophy hasn't been seen yet, and look at how that turned out for Dark Samus and Isabelle! And while Tingle shows up on the Great Bay stage, that's Majora's Mask Tingle. There's still Wind Waker, Hyrule Warriors, and Spinoff Tingle. There's precedent for this too! Train Link is still on the Spirit Train stage if BotW Link or Young Link is in the battle, he ONLY disappears if Toon Link fights. So that means Majora's Mask Tingle can still be a stage feature if Tingle shows up styled on Hyrule Warriors, the tingle spinoffs, or Wind Waker.
Plus he's one of the few recurring Zelda characters besides Impa, Beedle, and Skull Kid that reappears throughout Zelda. But I don't see Skull Kid with two games of his own.

KOOLOO LIMPAH BUCKAROOS LET'S GO