Stuffing obvious wave dashing is easy with down tilt. but that's as a read, if you throw it out and miss, you can get punished. Back air covers so many options, and stops a lot of luigis approaches, so get comfortable with that too. don't play near the ledge if he is stalling on it with Fairs. it's a pretty slow MU, so get comfortable with lasers to force approaches. And if all else fails, remember to cross up the shield if you ever approach a blocking luigi. no point in giving him free shield grabs, or risk getting nair'd out of shield if your pressure is lacking. also, if luigi is falling with his back towards you, don't chase him. you don't have anything that'll consistently beat his back air either.