I play Luigi and Ganon so, lets see
Luigi is running everywhere holy crap he is like a hyper active mouse with an extremely hardcore tech chase thanks to his wd and tornado. You have to keep in mind that his recovery is CRAP so knock him off and go for the edgegaurds, not to mention the knockback you'll do to him off a bair, or fair will be crazy
You're going to want to shffle your bair's and fair's like a monkey when he comes at you, the nair has more priority than you can ever imagine, and since he has a fast recovery don't try and go for long combos since most Luigi's will just smash Nair to stop whatever you're doing
Luigi will be going for grabs so keep him away from you. Do EVERYTHING in your power to knock him off the stage, once he's there he's pretty screwed, moreso if he doesn't use the down b recovery. The worse position he can be in is under the stage without a jump so try and get him there with your reverse, uairs
Just get used to playing the Luigi, it's a very weird character, no other is really like him (which is what makes it so fun)