Even though Waluigi is a god, I believe Shaggy would win in the fight.
Why would Shaggy win? Well, let’s remember that at on point (don’t remember where I saw it) he punched the freaking Joker! If he can punch Joker and live, why can’t he fight Waluigi and win?
If Shaggy really wanted to win the fight, he could just use 100% of his powers. Normally he only uses 1% because he doesn’t often fight anyone he finds worthy but if he believes Waluigi is worthy of his 100%....R.I.P Waluigi
(I would put more but I’m sleep deprived and can’t think straight lol)