So f*cking lazy!!! Jk, <3 you MoP.
Luigi's Mansion, a very nice cp. Hopefully your area doesn't have this banned!
As you should know, you need to destroy the pillars on top first then destroy the bottom pillars to kill the house. Unless you're facing a character who does very well with the house up like MK (b all day) or DK (down b all day), Ness benefits greatly with the house up.
As long as the to pillars on top are up, Ness can infinitely PK Fire the bottom ones. Get a lead in % and you can camp all day (not recommended on absorbers or counterers) like this. This will usually lead to your opponent getting pissed off and trying to destroy the top pillars, in which case you can punish their attacks on the pillar. Or your opponent will approach from above you, in which case their approach options are more limited than normal and you are usually in a favorable situation.
Another thing Ness does well with the house intact is setup missed techs. Any move that pops an opponent up like dthrow, uthrow, dash attack, utilt, usmash can bounce an opponent off the ceiling and into the ground. If they miss the tech they are open to almost any move, but the best of these options is usually to either jab lock or dtilt lock your opponent. If your opponent is good at teching it will be harder for you to set this up, but nobody is perfect so just be ready for them to mess up.
There are also some problems with keeping the house intact. Ness isn't the only one who can take advantage of missed tech, in fact there may be characters who can exploit the ceiling better than Ness. If you happen to notice somebody ****** you more than you **** them on the first floor, the break the house down.
Both you and your opponent will also have tough times killing each other inside the intact house. Learning to walltech can help save your life and prevent yourself from being *****. If the house ever gives you trouble killing your opponent, then by all means tear it down!
Once the house is down you can treat this stage like another FD. It does have a wall underneath it, so characters with glides/excellent recoveries won't be able to travel under the stage. A characteristic this stage shares with FD are those lame lips that eat vertical recoveries foe breakfast, be aware of this when recovering from below. And very tiny, ghost platforms appear sometimes, not like they make a big difference thoughsince they can fit like one character on them. Just another thing to know.