These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Luigi's Mansion: Dark Moon
8.8: GameSpot gave the game a score of 6.5. The Metacritic average is 86.
Not to mention the review itself was really strange. It mostly consists of glowing praise, only complaining about the check-pointing and one particularly frustrating sequence. Apparently it was frustrating enough to be worth 3.5 points.
The Brain, the final boss of the Scarescraper. Like all the other bosses, he's a King Mook with a special gimmick; in this case, Poltergeists. The Brain's gimmick is being able to charge up and release a sphere of energy to free himself from vacuums. However, Poltergeists already have the ability to attack while being sucked up, the charging can be interrupted by a power surge, and the energy sphere does no damage, giving no incentive to simply break the charge. In the end, he ends up being the second weakest of the four Poltergeist types.
Author's Saving Throw: For E. Gadd since in the original game he states he was turning ghosts into portraits for his art collection, when makes him come off as a Designated Hero since not only is there not any moral reason for it, but many of the ghosts he went after weren't even violent unless provoked. This game, most of the ghosts are friendly until the Dark Moon is shattered, and after it's reassembled and the ghosts go back to normal, he releases all of them.
Best Boss Ever: The very first boss: Grouchy Possessor (aka the one who possessed the spider queen), as well as the Final Boss King Boo. While Grouchy Possessor has the same weakness (lighting the web ball that hangs from the spider's web) that forces it out of its host, it changes the way you attack that weakness every time you damage it, while King Boo alternates between fighting you for real, and forcing you to run through an obstacle-filled course with him right behind you.
Demonic Spiders: While Gobbers are usually minor nuisances, they become this in Scarescraper's Rush Mode. There, they appear in certain rooms where whenever you try to use a predetermined door, one will show up and cause goop to appear on the door, with the only way to unlock the door being defeating it. Goobers have at least 100 HP at all times, and in Rush Mode, the time limit is so strict that you might run out of time. Even in groups, they're more likely split up in order to look for the goal, and by the time they regroup, time's up.
The little orbs that float around creating illusions. They have a tendency to scatter when they're revealed, will move around if they're not vacuumed up quick enough, and can hurt you if they pass through you. And if even one goes back into hiding, you have to do the whole process of revealing the hidden object and vacuuming them all up again.
The actual bats, along with spiders, mice, and beetles are perfect at harming and distracting you while you're busy sucking up the more dangerous ghosts.
Goddamned Boss: The Terrible Teleporters in the Scarescraper. A Dual Boss based off the Sneakers, their gimmick is spawning little funnels. These funnels will teleport you to another room, forcing you to walk all the way back each time. You'll only lose a few seconds generally, but it's still annoying
Distant Piano, which is odd because the actual Library Piano it's supposed to be a distant version of is rather catchy and not that scary.
Luigi has an in-universe case when the first mummy appears in C-2.
Hilarious in Hindsight: In one of the missions for the third Mansion Dr. Gadd tells Luigi to stop trembling in fear whenever he uses the teleporter, saying that they've "done this a dozen times" and there's nothing to worry about. Of course, he's proven wrong at the end when King Boo is able to sabotage it.
Moral Event Horizon: King Boo crosses the line when he destroys the Dark Moon, knowing that he'll force every ghost in Evershade Valley under his control, then creating a portal to unleash an army of ghosts to tear apart the fabric of the universe, and finally by putting Luigi through a horrific experience before they fight and gloating that Luigi, Gadd, and all of their friends are going to suffer the fate Mario did, which he's shown to be perfectly capable of doing.
Stop Helping Me!: Gadd constantly calling you to critique your work is probably the only weak point of this game. It gets annoying at times.
E-4's Big Boo boss if you're trying to get a 3-star rank on it, as you have to finish it within 3:20 without taking damage (or within 1:20 if you get hit exactly once). This can be an exercise in frustration as it means you have to trap a lot of Boos every time you manage to split up the Big Boo and avoid the other Boos' attacks while you're trying to aim a Boo at a cage. About the best thing you can do to ensure that you'll have an easier time is to try to catch as many Boos at once with your Darklight before you aim for the train.
Among the Scarescraper bosses, the Primordial Goo type bosses. Based on Creepers, they behave almost exactly the same, with the major difference that whenever a power surge is used, the Goo will fire a regular sized Creeper right at the Luigi who used it, and if he doesn't move out of the way, the Creeper will trap the Luigi, dealing a good amount of damage, and free the Goo, wasting time.
E-5. The level is simply running from room to room, catching the ghosts. However, you're on a time limit, and there are tons of ghosts. And once you beat them all, one final wave appears. This one is massive and contains dozens of ghosts who can easily gang up on you. Hope you practiced capturing multiple ghosts at once, because taking them on one at a time is an easy way to get yourself beaten up. Oh, and this is the one level in this mansion where you have to go out of your way for the Boo, meaning if you don't get it, you have to do the level all over again. There's a video here that shows one way to do it. (He does show you how to get the Boo first, which is definitely a good idea.)
E-4 if you're trying to get a 3-star rank on it, which in this case requires you to beat it within 3:20 without taking damage (or alternatively, within 1:20 if you get hit exactly once).
Rush Mode in general if you don't know how to find time pieces. The worst part is that everyone has to reach the end room, so it only takes one person who doesn't know what they are doing to screw it up for the entire team.
They Wasted A Perfectly Good Boss: After the battle against the Grouchy Possessor (see Best Boss Ever above), expectations were held high for the Harsh Possessor. The Haunted Towers theme is an overgrown garden of exotic and dangerous plants, and there are also two rooms devoted to crows. What form does the Harsh Possessor take? A giant carnivorous plant? A giant mother crow? Neither. Instead, a staircase. Yes, it was an unexpected surprise, but given the theme of the Haunted Towers and the expectations created by the Grouchy Possessor, it felt like a bit of a let-down.
Unwinnable by Insanity: You can lock yourself out of Treacherous Mansion if you play around with ghosts, teleporters and objects in the Nautical Exhibit. But you have to be really, really trying to pull this one off.
What an Idiot: Gadd. While he's clearly not there mentally throughout the game, the fact that he sold the King Boo painting at a garage sale really shows it. True, the Professor was led to assume that King Boo would need to be sent back through the Portraitficationizer, like Mario was, to be restored (little did Gadd- and us- know that Spirit Balls were kind of a thing King Boo could use), but being so careless with something so dangerous is still pretty bone-headed of him.