Oh, thanks for the input, Fly. There's no doubt that desynched blizzards and ice blocks are great for keeping Luigi out and camping - an indispensable tool, to be sure. Luigi doesn't really have sounds ways to muscle through those projectiles.
My earlier post on the Luigi-ICs match-up focused mostly on the advantages that Luigi has. I just want people to understand that I wasn't trying to skew anyone's perception of the match-up by only talking about the negatives for ICs. Rather, I was trying to mitigate the amount of unnecessary information brought to the table by filtering out aspects of the match-up that more or less cancel each other out.
For example, to address Fly's points on keeping Luigi in the air and shutting down his wavedash game with desynchs: Clearly ICs have a great uair that is well-suited for juggling and outprioritizing Luigi from below. Naturally launching Luigi with dash attack, uthrow, and dthrow upsmash sets up these kind of situations nicely. However, the power of this advantage is utterly made null by the fact that Luigi can employ the same tactics to at least equal, if not greater, effect. His chop is like designed to beat anything ICs have when they're above him, seeking to regain their feet. Luigi's uair also has amazing priority, similar to ICs' uair. It will beat ICs' dair, nair, fair, or any other aerial, fast-fallen or not. Luigi can set up this scenario with launchers, just as ICs can set it up on him. Luigi's dsmash, nair, and throws all prep beautifully for air chasing. So how is ICs' uair chase game any more useful than Luigi's? Not in many ways. Effectively, both sides benefit and suffer equally.
As far as desynched ice blocks and blizzards are concerned, they don't pose much of a threat to a wary Luigi. Sure, blizzards lead handily into grabs, upsmashes, and dash attacks ... if they hit. But Luigi's not going to be haphazardly wavedashing into your blizzards. Rather, he's not going to even give you time to setup a desynch. Even belay oos -> blizzard (to those knowledgeable in ICs' desynch tricks), doesn't grant enough time to ICs to initiate a desynch before Luigi comes plowing through with a dsmash, which unavoidably (now that Nana is airborne and Popo in the frozen up-b animation) hits one or both of the climbers. Ice blocks do great damage. However, Luigi should be able to SH around them fairly easily without putting himself in harm's way, since he has his aerials to defend himself from wavedash fsmashes and derivatives (which are significantly less useful during desynchs, since only one climber is able to charge in at a time, and the human shield effect is non-existent).
Luigi merely has to bide his time until you mess up a desynch, you grow impatient, or he finds some kind of opening. He lands a dsmash, and from there he proceeds to separate and KO Nana and/or Popo with relative ease.
If the ICs player is significantly better than the Luigi, then sure, get your reads and hard counter all of Luigi's skirmishes. However, on an equal plane, the simple fact is that Luigi doesn't need to predict so much as react to where ICs are and use safe moves fast enough to exert pressure, comboing once he lands a hit. ICs perish if they don't out-think the Luigi on another level.