If there is one problem with Mario that I've noticed, it's that most of his finishing moves require a solid set-up to be effective, and this can be a problem if your over 180% damage and facing off against a strong character (which is usually the case for me). What I do to overcome this weakness is spam the Mario Tornado close to the ground, as well as caping, uppercutting, and the 1-2-3 combo while rolling once or twice inbetween attacks. As long as you time your hits well and be sure not to get nailed when you come out of your roll, your opponent's damage will skyrocket. If playing a one-on-one, just after the one-two part of the 1-2-3 combo, do a quick side smash move with the C-stick when their damage is over 130% to send 'em flying. same goes for a multiplayer match, but you need to watch your back during the rolls and might want to try using an up-smash rather than a side smash. I can't stop using Mario's meteor smash, but if you plan on using it, take into account both the vunerability prior to the punch (not to mention you can barely move for a second or two afterwards) and the precision needed to send your foe flying downward (there's quite a delay after you input the command and the actual attack).