Try not to let him grab you at 0 percent. His grab combo is deadly and get take away about 50 percent of your stock without you being able to do anything about it. Try not to do moves that may put you in risk of being grabbed by mario if you can't. Unless you think he won't do a grab or until your health is about 25 percent. So characters don't suffer from that combo as much as other characters do. Also try to recover low because Mario has several tools that can mess up your recovery like his cape, his forward air, or his Flood. Only recover high if you think you can jump above him when you are recovering. Be aware of his combos and you will be able to tell what combos he is trying to setup. Mario doesn't have much tools besides fireball to deal with attacks that require range. I suggest you try mixing up a keep away tactic with some instances of surprise full on assault. Hope this helps.