From my experience, playing Luigi is pretty lame. Use needles to force them to approach. His wd can be slippery, and he'll try to bait grabs using it. Wait for a wiffed aerial, punish with a grab to a fast fair. Use up air a lot. Don't use tilts if you think he could nair out of hitstun, or else it will trade and you will be above Luigi. In my experience, I like smaller stages to give him less room to move around, and keep him on plats.
Edge guarding can be tricky, watch when they jump and when they down b in neutral so you know if they have those options. You can use the Marth killer against Luigi as an edge guard, but try shino stalling until he gets close, and roll up a bit earlier than you would think, otherwise he will up b you, and when you click "R" you will airdodge (alternatively you can standard get up). Grounded needles add on percent, bair from the ledge hardly ever works, so I would honestly suggest keeping center stage and refreshing ledge invincibility with shino stall (can bait a jump, down b, or up b). Advance strat would be to just have your back against the ledge off stage, so when he up b's, you can grab it before him.
tl;dr keep stage, use needles to add percent.
Since Luigi has no hitstun, you never want to tilt/dash attack/ ever approach ever when he's at a low% (He will nair you). Dash attack is kind of a hard read since his movement is so slippery. Always use down throw, and mix up fair/up air. At low percents, you can shield and see if they space aerials on your shield after a down throw, if not then you get another grab. Luigi will also wave dash in and jab your shield, when you see this, he's baiting a shield grab. If you fall for it, he gets an easy up b.
When recovering, you always want to go to the platforms imo. Most he can get is an aerial, and if you DI it, nothing else. If you land on the stage, he can react with ledge dash up b. I prefer hiding my second jump and air dodging, but mixing it up with double jump fair if he losing his invincibility on the ledge.
Last thing would be when you're in your shield, Luigi loves doing 2 aerials on shield. His aerials don't have much lag, and your best option would be a very fast nair oos, or wait for the second aerial and escape to a platform, or else he can get a grab and react to a roll.
First time posting on the forums here, hope I helped a bit.
