You can eat his projectiles, but that's not a super viable option most of the time because of how fast YL can send death flying at you. I think the Wario YL matchup is about even, Wario lives way longer than YL and has way more consistent kill options but YL can give Wario hell the whole match and if Wario isn't careful he's gonna lose.
Wario already doesn't have shining approach options, so having to approach a character that can lock down so well definitely can be a problem, but at the same time Wario scares people, for good reason. Later into the match you're never ****ing safe from the little ******* running up to you, whiff punishing with UTilt, then farting you into the blast zone.
You're gonna have to play smarter than you usually do, rely on Wario's weird / tricky movement to fake YL out and then start locking them into Wario's combos (he has too many to mention specific ones) to rack up percent, repeat until you get a kill opp. Offstage I'm gonna say, don't bother. YL is gonna win out most offstage exchanges and could even kill you, so you're best off using the bike to edge guard or waiting at the ledge and DTilting or something.
Now that I think about it, you may even be able to call this MU in YL's favor, but not by a lot. Wario's only real lacking front is approach options, and YL is pretty good at remaining noncommittal. The good news is, he can't really camp you well because you can just sit there and heal off of it (if he's defensively zoning / camping you, eating his projectiles becomes way easier) indefinitely while building up waft which is always a massive threat.