Pick another character if you want to win a tournament set.
But if you choose to go Mario, basically don't let him take you to any stages you're unfamiliar with. Camp as much as possible and try to outspace him with tilts, B-air, and F-smash, or try to bait him into your Jabs at close range and then Jab cancel into mixups. Your safest option for stopping the Tornado is also fullhopped fireballs as well, which will hit him as long as you can hit the top.
Gimping him is possible, but extremely risky. You can do it if you call a Tornado recovery and Cape it, or if you know exactly when and how he's going to Shuttle Loop. Fireballs, FLUDD, and creative edge tactics are also necessary if you want to edgeguard him. If he does a glide attack, N-air clashes with it. N-air trades hits with his Up-B, but it's not favorable and should only be done when you have no other options.
imo the matchup hinges a LOT on how much you're able to F-smash him, and how much you can Jab him before he grabs you.
If he's above 110% and your Up-smash is fresh, watch out for his Tornado for a free opportunity to Up-smash him out of it.
If he does repeated D-tilts on your shield, you can D-smash out of shield between hits if you buffer perfectly.
Your biggest problem in general will be dealing with his F-tilt. If he delays hits intentionally, it will be a guessing game to punish it.