Few things I should point out about Jdietz's post:
-I wouldn't recommend jab-> up b against Wario since it's never guaranteed. He can easily SDI down on the jab to avoid the up b.
-I honestly wouldn't recommend using rising down b out of momentum canceling either due to Luigi's Horrible horizontal aerial speed. You don't necessarily have to side b after momentum canceling, but make sure that you mix it up with some of his aerials.
Tips:
-If you're ever above your opponent while they are on the ground, avoid falling with a nair unto their shield.
-Grab releasing Wario should never work (Wario just has to hold down) with Luigi unless Wario is dangling in the air. Even when you have a chance to grab release him, an up tilted F-smash is much better to use over an aerial up b.
-Mix up your short hop air game a bit more, You shouldn't always double aerial whenever you short hop because it quickly becomes punishable. Try something like short hop d-air, then a buffered d-smash. You have tons of options from that point so it's up to you to choose.