Okay, this is MY idea for how to make Luigi feel more "Luigi's Mansion-y".
Neutral Special: Poltergust 5000
Even though his Green Fireballs were decent projectiles, I think we need something that truly represents Luigi. When Luigi holds down the Special Button, Luigi takes out the Poltergust 5000. Once Luigi has taken out the vacuum, Luigi's movemet changes to like when a character grabs the Cracker Launcher. If someone gets in range of Luigi while in this state, the vacuum will lock on to the enemy (you can also lock on to multiple enemies). The enemies will take damage overtime in this stage, so they have the choice of to fight Luigi head-on and risk more damage or run away quickly. Also if they don't get out of range within 6 seconds, they will get sucked in and shot out resulting in 22% with decent knockback.
Side Special: Green Missile
Don't worry, nothing has changed.
Up Special: Super Flutter Jump
Super Flutter Jump is very similar to his old special, with the exception that you will slowly decent with kicking of your feet like in SMB2/SM3DW. You can of course hold down to quicken your decent in case if you're in a tight spot.
Down Special: Luigi Cyclone
Again, nothing has changed.
Final Smash: Ghost Rush
Luigi takes a deep inhale and whistles very loudly, this calls out ALL of the good ghosts from Luigi's Mansion: Dark Moon to come out and start a riot on the enemies. While the ghost rush is going down, Luigi is just playing with Polterpup.
Forward Smash: Strobulb
Luigi now has a special new Forward Smash which stuns the enemies. The longer Luigi charges it, the longer the enemy is stunned. This combos very well with his Up and Neutral specials.