Waluigi's issue is he can't get past Low-Godly.
How can Waluigi use his teleportation, time manipulation, or transmutation? If he can BFR via Teleportation, leave Popeye incapacitated via being frozen in time long enough, or transmute him into something harmless, he can win. But his profile doesn't detail how he has those abilities, as far as I can tell, so I don't know if those are strats he could use.
Does Waluigi have a Mega Mushroom or Starman?
Although, funnily (& as you'll see, disgustingly) enough, Waluigi may not actually need any of that to win:
- Whiskered Eggplant: Waluigi throws an eggplant which causes peoples that come in contact with it to vomit uncontrollably
Popeye being
High 4-C is with spinach. If he hasn't completely digested it, vomiting could cause him to lose his spinach, making him revert to where he's only
At least 9-B.
Unless Popeye's invulnerability protects him, if Waluigi uses the Whiskered Eggplant & it works, Waluigi could become able to oneshot Popeye. (All the vomiting would also hurt Popeye's strangely Unknown Stamina, too. Waluigi's, by comparison, is Very High.)
Alternatively, there's the weakness of Popeye's spinach power having a time limit. If Waluigi can survive that long, he could win. And he probably can with his stamina & abilities. Against Waluigi on the defensive, Popeye doesn't have many advantages other than Flight & maybe his Toonforce.
So for now, it seems like Waluigi has the means to win.