Luigi's Mansion: Dark Moon (Luigi's Mansion 2 outside of North America) is a video game on the Nintendo 3DS, and a sequel to the GameCube launch title, Luigi's Mansion. It was developed by Next Level Games, which previously collaborated with Nintendo on Punch-Out!! for the Wii, and was released in North America on March 24, 2013.The story finds Professor E. Gadd researching the ghosts of Evershade Valley, but when King Boo shatters the Dark Moon the formerly friendly ghosts start running amuck, and itís up to Luigi, armed with the Poltergust 5000, to solve this paranormal problem.Unlike the first game, which took place almost entirely inside the eponymous mansion, there are multiple areas to explore, including a snowy mine and a clockworks in a desert. Luigi has a greater amount of items and power-ups at his disposal, including a strobe function that can stun multiple ghosts simultaneously (as opposed to having to shine the flashlight on one at a time).In February 2013's Nintendo Direct, this was revealed as one of several "Year of Luigi" games to be released in 2013, along with Mario & Luigi: Dream Team and the New Super Luigi UDLC for New Super Mario Bros. U.
This game includes examples of the following tropes:
Absent-Minded Professor: Gadd has even worse bouts of this than he did in the first game. In one scene, he can't even remember how many Toad assistants he has (made all the more serious by the fact that King Boo is holding them hostage.) It almost enters Mad Scientist territory, as E. Gadd is seemingly even more erratic and scatter-brained than usual while sending Luigi out to once again capture hundreds of spirits if not thousands in his name. Although he's so old that Gadd may simply be going senile, if he wasn't already.
Animated Armor: Present in Gloomy Manor. They'll try to cleave you when you get close to them, and may block your path. In Treacherous Mansion, Greenies can possess them and use them to attack Luigi. The Tough Possessor uses them as hosts, and ultimately possesses a huge one.
Arc Welding: King Boo, who it turns out was directing all the previous monsters that appeared unconnected.
Gadd worries that the absence of the Dark Moon will make the ghosts go crazy, cause worldwide terror, and worst of all, ruin his research.
Invoked once more in A-5's Description. "They're blocking our progress AND they ruin the furniture AND they're just plain gross!"
Artifact Mook: The Carnivorous Plants show up in Treacherous Mansion for no real reason, including one that just happens to be sitting in a cupboard. Given that they're probably genetic experiments or something, you just have to wonder how they got all the way across Evershade Valley to a mansion in a middle of a ravine.
Artifact Title: Luigi explores various different places in this game, rather than a single mansion as mentioned in its predecessor's title. None of them are owned by Luigi to boot, and only two are even legit mansions. The titular Dark Moon, however, is your Plot Coupon, and thus is fairly important.
Bag of Holding: Lampshaded by E. Gadd after giving Luigi a particularly big key item, commenting that it's a good thing Luigi has such deep pockets.
Best Served Cold: The whole plot is King Boo's revenge plot against Luigi and friends. Note that this time the villains are putting the protagonists in paintings (he only mentions Luigi, Mario, the Toads, and Gadd as targets. Whether he has plans to do this to anyone else is uncertain.)
Big Boo's Haunt: In a sequel to Luigi's Mansion, what do you expect? The first area, Gloomy Manor, is just a typical haunted house, but the others are a cross between this and other classic Videogame Settings.
Luigi's flashlight — which, in this game, is used like a dazzler in order to stun ghosts. Some ghosts are wearing sunglasses that must be vacuumed before the light can be shined at them. Others carry objects or wear buckets and the like. For these, you have to either wait for them to attack before stunning them, or shine them with your Darklight, which will make them taunt and open them up to a strobe flash.
Some small creatures that aren't ghosts (like spiders, mice, and bats) can be destroyed by the flashlight, which sometimes turns them into Hearts, coins, or bills. Golden versions of these creatures yield more valuable treasure when killed this way.
On another note, here's a good safety tip for this game. A fully-lit room is usually safe. (Safe to a point; they might have something dangerous in it that isn't a ghost.) However, a dark room more than likely has ghosts hiding in it somewhere.
Bond Villain Stupidity: There are a few background scenes that suggest that King Boo is capable of ambushing Luigi several times over the course of the game, suggesting that this whole thing is sadistic "fun" to him. (Much like it was last time.)
Bonus Level: Each Mansion has one, which is unlocked by catching all the Boos in the first five missions.
Bonus Stage: A few missions have these, where a door lets Luigi access a special area where a Mini-Game is played. A couple of them require him to collect every Red Coin, another requires him to capture all the Gold Greenies in a giant hourglass that is filling with sand, and another requires him to win a snowball fight with three Hiders. All of them have a time limit. The only real tangible rewards are treasure (and in a few cases, Gems).
There's something like this in the D3 mission. At one point, Luigi has to defeat a Super Greenie, a Super Slammer, and a Super Gobber to gain access to a door. The Super Gobber is the one to watch out for. It has 300 hp (as opposed to most Super Gobbers, who have 200) and is harder to hurt. In fact, the only reason this isn't literally a Boss in Mook Clothing is because the Vault does not distiguish it from other Super Gobbers.
Earlier in the game, a Strong Sneaker acts as a miniboss that holds the last piece of a giant clock mechanism in Old Clockworks. Unlike a normal Boss in Mook Clothing, this Strong Sneaker is weaker than the ones found later in the game (Barring D-2 and E-5), but it sits in the sidelines while it sends regular ghosts at the player once it's cornered (it does have one clever tactic; this is the Escort Mission, and it can grab hold of Toad and use him like a shield, making itself impervious to Luigi's flashlight for a few seconds.)
Boss-Only Level: The boss missions qualify, with the exception of the Haunted Towers boss, which has a long staircase puzzle before the fight.
Cerebus Syndrome: With regard to the enemies - the Boos at first are amusing and punny, but later on they actually become quite sinister by the fourth and fifth mansions. A key scene is in D-2 in the crystal mine where they are experimenting to make the other ghosts tougher and more vicious, and said other ghosts are visibly scared of them. King Boo is also far more evil in this game than he was in the first.
Cerebus Rollercoaster: The music. The main theme is catchy and soft, while some of the rest of the soundtrack would fit right in with a less family-friendly work.
The Chessmaster: King Boo. The opening of E-3 makes it plain that he knew the whole time you were spying on him and was spying right back at you, and then lures Luigi into the train exhibit to make him fight the Big Boo. On top of shattering the Dark Moon so that he would have an army of minions and would keep Luigi busy.
Console Cameo: E. Gadd gives Luigi a modified first generation Nintendo DS in the opening cutscene. (He later calls it the "Dual Scream".) It serves as the source of the maps of the mansions and as a means of communication between Luigi and E. Gadd, similar to the Game Boy Horror from the first game.
Looking at the promotional art, King Boo has a new crown. Hope it's more valuable than his last one, which was worth only one gold coin. It's a powerful magic item, but to Luigi, it's worthless. He does take it at the end, but it does not increase his money at all.
Luigi keeps the map he used to find the mansion in the last game on his mantel.
Luigi actually lives in the rebuilt mansion from the first game. Apparently the Rank D mansion is the canonical onenote not quite as bad as it sounds; the lowest was Rank H.
Luigi still shows that first boss ghost who's boss!
E. Gadd mentions having carelessly given King Boo's portrait away at a garage sale to hand-wave his escape and presence in the game.
A Big Boo appears as a boss and is fought in a manner similar to the previous game's Boolossus.
One of the Boos introduces itself as JamBoolaya and demands not to be called GumBoo, the latter being the name of a Boo found in the original game.
E. Gadd nostalgically reminisces about his and Luigi's last adventure early in the game.
E. Gadd once again gives Luigi a communication/map device based on a Nintendo handheld, a DS this time.
Co-Op Multiplayer: The ScareScraper, which has up to four players trying to ascend through the building by either catching all of the ghosts, having everyone search for and stand on a set of switches in time, or chasing Polterpups depending which game mode is chosen.
Cosmetic Award: Getting all the Gems in a Mansion gets you a statue in E. Gadd's Vault; it's kinda cool, but doesn't give you any real benefit.
Creepy Cemetery: Can't have a Haunted House-style game without one of these, right? There's one in the Haunted Towers. (Oddly enough, the only Mooks you have to worry are a few crows and a Golden Greenie, but this is where a Boo is found and a Mini-Boss battle is fought.)
Cuteness Proximity: Nobody can really stay mad at the lick-happy ghost dog, despite the trouble it causes trying to play. Luigi seems to have taken it in at the end of the game. The fact that the dog is the ghost which gives Luigi an extra life if he finds one of the Golden Bones kinds of helps you like the little guy.
Cutscene Incompetence: Whenever Luigi prepares to do something and the scene changes to a cinematic, odds are things are going to go badly for him.
Darker and Edgier: The game starts out about as light as the first game, but as King Boo's plans and motives start being revealed, the game gradually gets darker.
Dark Reprise: When Luigi sees Mario stuck inside King Boo's painting, the theme song for the entire Mario franchise plays in a more gloomy tone.
Dark Is Not Evil: The Dark Moon is, despite the name, a Restraining Bolt on the ghosts. Rebuilding it is part of the game. Also, most of the ghosts in this game were actually pretty decent guys before King Boo came and started to cause trouble. In fact, after the battle with the Three Sisters, Professor Gadd remarks that they were very polite and courteous before all this happened, and remarks that he'd like to invite them to "ghost tea" once the situation resolves. (And he does just that, during the end credits.)
Deadpan Snarker: E. Gadd does this through the whole game, sometimes at Luigi's expense.
Demonic Possession: Each of the main bosses except King Boo do this (which is natural, considering they all have the word "Possessor" in the names), possessing a creature or object to fight Luigi. Each Boss Battle requires Luigi to force them out of their hosts somehow to use the Poltergust 5000 on them, and this must be repeated multiple times (one shot won't do it).
Development Gag: The fact that it's on the 3DS is probably a reference to the fact that the Gamecube was meant to be a 3D console, and the first Luigi's Mansion was supposed to showcase that.
The Dev Team Thinks of Everything: Wonder why the cutscene travelling through the Pixelshifter is unskippable? Because when you come back from the Tough Possessor boss, King Boo traps you and brings you to his realm, so people who skipped it wouldn't understand why it's significant. And if they skipped that cutscene... they'd be completely lost.
Does Not Like Spam: The Man Eating Plants aren't ghosts, and are thus immune to the Strobulb and Poltergeist 5000, but Luigi can defeat them by tricking them into eating a spikey fruit that often grows nearby.
Dramatic Irony: We know King Boo is the Big Bad right from the opening cutscene, but Luigi and E. Gadd don't find out until much later.
Dub Name Change: Outside of America, the Poltergeist bosses are known as Boffins, the ScareScraper is called Thrill Tower, and some of the levels have different names (such as the final boss, which is changed from "A Nightmare To Remember" to the straight-up "Shatter The Illusion").
Endless Game: ScareScraper Mode, if you set the number of floors to infinite.
Escape Artist: The first two times Luigi captures the Polterpup, it escapes from the Poltergust 5000 before he can put it in the Vault. Fortunately, Professor E. Gadd manages to make an improvement on the device after the second time, and it stays put after he catches it the third time.
Escort Mission: Luigi has to rescue Toads in several missions. They can't be harmed, so it's more a matter of navigating them past obstacles. If Toad is too scared to follow Luigi, and he often is (each one seems very afraid of something that is common in the Mansion he's in), Luigi can carry him using the Poltergust 5000 and even use him like a projectile.In the rescue mission at the Treacherous Mansion (the hardest Mansion), Luigi has to escort two Toads.n.
Expy: A few of the ghost types are expies of ghost types from the first game.
Greenies are similar to the golden ghosts.
Slammers are similar to the blue twirlers.
Gold Greenies are similar to the speedy spirits.
Females Are More Innocent: After Luigi beats the Three Sisters (the only female ghosts in the game), E. Gadd says that he is kinda shocked to see them behave so violently, what he doesn't even bother to say about any other ghost in the game.
The boss of the Gloomy Manor has a swarm of spiders helping it (which can actually benefit Luigi, because if spiders are hit with the flashlight, they might turn into Hearts).
The third boss is a 12 wave endurance match against all the ghosts you've faced atop the clock tower.
Bosses in the ScareScraper always have normal ghosts assisting them. The reason for this is to keep the other players busy so that everyone can't just gang up on the boss.
The Fourth Wall Will Not Protect You: An in-universe example. When you examine the security image before E-3 you see the identity of the final boss, only for him to turn round within the static image and laugh terrifyingly before making the shot fade to static.
Fun with Acronyms: The first letters of the five "mansions", the adjectives describing their possessors, and their unlockable ghost hunt missions spell G-H-O-S-T. And if you add in the ScareScraper, it spells ghosts.
The Possessor ghosts follow this trend as well: Grouchy, Harsh, Overset, Shrewd, and Tough. Also, in the Dutch and German translations, you get SPOOK and GEIST, respectively.
Game-Breaking Bug: The key glitch, where a necessary key fails to spawn in multiplayer and hence the run is unwinnable. No one knows what causes it.
Get Back Here Boss: The fourth boss is constantly fleeing from you, with you giving pursuit in a bomb-launching sled.
Giant Foot of Stomping: Excluding cinematics, all you see of the Tough Possessor's final suit of armor is two of these and a floor-piercing sword.
Giant Spider: The Gloomy Manor Boss. Nasty. Well, truthfully, the true boss is the Grouchy Possessor, who has taken possession of the spider.
Going Through the Motions: Luigi has a few animations (most of them cowering in one way or another) while he's face-to-face with Gadd. Over the DS, he always has a "hmm mmm" expression even when Gadd is saying things that should be terrifying him and always lets out a big shudder when done with the call. Luigi always cowers with Gadd laughing every time he's sent through the pixelator, which Gadd lampshades at one point.
The Goomba: Greenies. However, they get much smarter - for Mooks - as the game progresses; as early as the third mission, some of them use garbage can lids as shields, making them harder to stun, and in the fourth mission, some of them wear sunglasses, making them impossible to stun unless you first use the Poltergust 5000 to get rid of the glasses. Even later, they disguise themselves as mummies or haunted suits of armor, making themselves untouchable until you can expose them.
Green Thumb: Although there are a few monstrous plants to deal with, several plants are useful here, much like the first game. Using the Strobulb on flowers will usually yield treasure, and watering small shrubs can sometimes cause them to grow into beanstalks that Luigi can use to climb to rooms he couldn't previously access.
Pressing a direction on the D-pad will make Luigi call out for anyone in a mansion ("Hello?" "Yoo-Hoo?"). Once Luigi discovers that Mario was kidnapped, Luigi's cries to the unknown will change to the cries for Mario from the first game.
Multiplayer uses the same feature as its primary form of communication between remote players by incorporating phrases such as "Help help" and "Good job".
Hoist by His Own Petard: In order to defeat King Boo in the Final Battle, Luigi has to fool him into hurting himself. If Luigi positions him so that one of his own spiked balls falls on him, he is stunned for a couple of seconds, letting Luigi use the Poltergust 5000 on him.
Improbable Weapon User: The Greenies typically arm themselves with things like shovels and rolling pins, along with garbage can lids to use as shield, basically anything that could plausibly be used as a weapon in the area they're in (although they sometimes use actual weapons too, like swords and, in one area, spears).
It's Personal: When King Boo finally meets with Luigi face to face it's clear that this time, despite his composure, that he's really pissed. This combines with some Terms of Endangerment to create some really quite creepy dialogue.
Hey, if isn't my old pal Luigi. Or is it Baby Luigi? I can't tell the difference. Remember when you sealed me in a painting for all eternity? Good times.
Subverted in the intro sequence. A Greenie is shown approaching Professor E. Gadd from behind, but as it turns out, he doesn't actually want to scare him.
In E-2, Luigi unlocks the door to Treacherous Mansion before turning around apprehensively, at which point King Boo appears in the doorway behind him and vanishes before being noticed. Later, in the intro to E-3, when you examine King Boo in the final security snapshot, he abruptly turns toward the camera and laughs.
Kill It with Fire: Luigi can't turn the Poltergust 5000 into a flamethrower like he did with the previous model, but he makes use of torches, candles, and combustable fuel often, mostly in places where there are a lot of spider webs or ice.
Killer Rabbit: Most of the enemy ghosts. One variety is described as having a fondness for cuddling, which they express by violently absorbing Luigi into their gelatinous bodies. Boos have pretty much always exemplified this trope, but they now squeak upon receiving damage and being sucked into the Poltergust.
King Mook: Besides King Boo (of course), the main game has the Ancient Poltergeist and the Tough Poltergeist. In the ScareScraper, every fifth floor has one or two of these, the last floor always has The Brain (another Poltergeist boss). Each of the Scarescraper bosses add gimmicks; Greenies carry huge bombs and drop smaller ones while being vacuumed, Slammers have regenerating shields and summon Beetles, Sneakers create teleporters to other rooms, Creepers and Gobbers can create other Creepers, and The Brain can free himself from the Poltergusts.
Knight of Cerebus: King Boo is much more of a threat than he was in the last game, and is even scarier than before, rivaling even the RPG villains for the title of Most Evil Mario Villain.
Lampshade Hanging: Prof. Gadd provides this (naturally, since he's one of the only two talking characters), such as the way the same cutscene plays when Luigi pixelshifts to a level ('You don't have to cower in fear every time, you know. You've done this over a dozen times and nothing's gone wrong.'), the way they're stuck with each other in the same small bunker, and the way Luigi can carry big items around with him (see Bag of Holding).
The Gold Greenies only appear if you search in certain vases, drawers, etc., and once you find them, they run around you in circles. (Except for one area in the Haunted Mine where there are two of them that attack Luigi.) They give out a ton of cash when you suck them in, so it is worth looking for them.
A lesser version comes as gold-colored versions of minor enemies such as spiders and mice, which usually drop a gold bar or a wad of dollar bills if you use the flashlight on them quick enough.
Milestone Celebration: Part of Nintendo's Year of Luigi, the 30th anniversary of Luigi's debut in Mario Bros.. Incidentally, the inclusion of Luigi's Mansion just happened to be by chance, since it wasn't developed for the anniversary in mind. Nice coincidence, eh?
Money Spider: If you finish off a ghost with a charged vacuum suction (by pressing A), you will get money for catching it. The higher the meter is charged, the more money you get. You also get more money for catching multiple ghosts simultaneously.
Multi-Mook Melee: In the final level before the boss in Treacherous Mansion, the timed ghost hunt culminates in a fight with a horde of over 20 ghosts, who come in waves from the portal on the Terrace.
Museum of the Strange and Unusual: Treacherous Mansion, though the exhibits aren't actually strange as much as haunted and possessed due to the place being a favorite haunting ground of ghosts.
Murphy's Bed: In the first mansion. When Luigi sits on the rather large bed in one of the rooms, it swings up against the wall that the headboard is adjacent to, tossing the poor guy into the next room. This is needed to progress in a couple of missions.
Nice Job Breaking It, Hero: Apparently, E. Gadd is partially responsible for this mess, having accidentally given away King Boo's portrait at a garage sale (kind of makes you wonder how secure all the other ghosts Luigi caught in the first game are...)
No-Nonsense Nemesis: King Boo is made so much more menacing since he adopted this attitude. Justified since his revenge is what kickstarted the game's plot.
Nonstandard Character Design: The Boos are the only ghosts in the game that don't glow, and they're also the only ones who appear opaque when not completely invisible altogether.
Gadd has one when King Boo abducts Luigi in the Pixelator.
Luigi gets his fair share over the course of the game too, but the best example is when King Boo gets sucked into the vacuum, only to pull himself back out.Twice. Complete with what is probably the closest thing a Boo can do to a Slasher Smile. Luigi's fear is pretty justifiable at this point.
Our Ghosts Are Different: Obviously. E. Gadd implies that ghosts have the ability to evolve and adapt like living things, and many of the spirits native to Evershade Valley are unlike any he's ever encountered. Boos are apparently different enough to have their own container separate from all the other ghosts Luigi captures and sends to the Vault.
Pass the Popcorn: Gadd claims he did this while watching the Boss Battle of Haunted Towers. Fortunately, he takes the rest of them a little more seriously.
Peek-a-Bogeyman: In the garage, a mook is seen scaring Luigi by jumping out of an old-fashioned car, then laughing about it.
Plot Induced Illness: In the ScareScraper mode, there is a curse status effect that reverses your controls and can only be cured by using another player's Dark-Light. It comes complete with coughing from the player and is contagious, too.
E. Gadd's Pixelator, which is used to link the five areas to his bunker.
Later levels also have more traditional portals, but they only work in pairs. The final mansion has a central room with six teleporters connected to various parts of the mansion, though.
Punny Name: Like last time, all the Boos have puns for names. Several of the levels do as well, such as A-5 (A Sticky Situation), C-5 (Piece At Last), and the final boss (A Nightmare To Remember, at least in America).
All the floors in the multiplayer mode are randomly generated (including the types of enemies found within).
Intrusion Missions use the normal mansion layout, but the enemies appear in random rooms.
The smaller cobwebs you need to suck up in "A Sticky Situation" are randomly generated each time you visit the level.
Reality-Breaking Paradox: In the "Paranormal Chaos" mission, King Boo creates a portal that summons a horde of ghosts, which threatens to create an effect like this unless Luigi can defeat the horde within a time limit (seeing as this is a Timed Mission, it is implied that it happens if you fail to do so.)
Recurring Riff: The classic theme from the GameCube version returns in some scenes. Otherwise, the soundtrack is more varied this time around.
Recursive Reality: At one point, you can find a dollhouse with windows you can look through. If you do so, you see the very room that contains the dollhouse, with Luigi looking through the window. A circular spotlight suggests that it is Luigi looking through the dollhouse window at himself looking through the dollhouse window. Mind Screw, much?
Ridiculously Cute Critters: The Toads, even more so than in other games. They're prone to hugging Luigi upon rescue and high-fiving him after solving a puzzle, make a squeaky noise like a soft toy when walking around, get scared easily and cry if they're separated from Luigi for too long, and yell "Wheeee!" if you send them flying with your vacuum.
Luigi falling in a different way almost every time he is transported by the Pixelator.
Luigi celebrating after defeating each boss only for something to appear and startle him.
Sealed Evil in a Can: Luigi did this to King Boo in the first game... suffice it to say the can didn't last long. And was apparently rather shoddy, since King Boo broke out by himself before he even found his new crown.
Suddenly Voiced: This is the closest the series has gotten to full voice-acting since - while the characters don't directly speak their lines, they have some clear English phrases. This is most noticeable in the ending, when Mario congratulates Luigi.
Super Cell Reception: Zig-zagged. The Dual Scream has pretty bad reception when Luigi goes underground, but it works perfectly fine when he's in an alternate dimension.
Tempting Fate: Before starting one of the missions, E. Gadd jokes to Luigi that he doesn't have to cower in fear every time the Pixelator starts up, as he's used it a dozen times and nothing went wrong. After the battle with the Tough Possessor, the Pixelator is hijacked by King Boo to beam Luigi to his own dimension. The resulting Oh Crap from Gadd after he sees that Luigi didn't return carries a hint that Gadd thought it was his fault.
Theme And Variations Soundtrack: The music that plays in each mansion is a variation of the same melody, arranged and orchestrated differently. Here's a few examples:
Glooomy Manor has a bass clarinet melody accompanied by piano and plucked strings.
Haunted Towers has a pan flute melody accompanied by low strings, marimba, and a tribal drumbeat to create a more adventurous atmosphere.
Old Clockworks has a harpsichord melody and pipe organ harmony to create a more classical and refined atmosphere. Clockwork Ruins, on the other hand, is an Egyptian style remix, fitting for the environment.
Secret Mine has the melody played on bells and a quiet electric bass harmony to create a mysterious atmosphere.
Numerous Ghost Themes, thesetwo for example, take on the main melody.
Theme Naming/Hurricane of Puns: The Boos once again are all puns with the word "Boo" in them. In addition, the "Possessor" ghosts that serve as the bosses each have an adjective one would often use to describe a college professor, such as "Harsh Possessor", "Tough Possessor", "Grouchy Possessor", etc. In addition, putting the first letter of each of the Possessor's names spells out "GHOST".
This Is Gonna Suck: Nicely summarizes Luigi's demeanor throughout the whole game. Also his reaction to the fifty-foot living knight armor boss.
In the first game, King Boo couldn't battle you on his own; he needed the False Bowser suit. Here? He's firing lightning bolts all over the place, changing size to crush you, becoming intangible, ramming you, and executing divebombing tackles that cause steel spiked balls to rain from the sky. "Fight you like a true Boo", indeed.
The Boos in general are much tougher than last time. In the first game, about half of them couldn't attack Luigi at all, and even the ones who could (other than Boolossus and King Boo) usually chose to run from him anyway. In this game, the Boos hide while invisible, and attack Luigi using dangerous ambushes from the shadows (having said that, once you get used to their MO, fighting them isn't all too hard.)
On that note, Professor E. Gadd himself has taken a few levels. The upgraded Poltergust, that completely blows the last model out of the water? His doing. Replacing the fragile process of turning ghosts into portraits with ghost-sealing canisters? His idea. Creating means on the fly to repair and replace necessary items to get through the mansions that the ghosts periodically destroy? He's got that. Heck, a teleporter that only requires a monitor and security camera? Take a guess.
In-game example: Most versions of the Mooks have a stronger version that appears later in the game.
In comparison to the first game's ghosts, Dark Moon's ghosts are much more crafty and resourceful in general, even without being powered up. The Greenies in particular especially show it, equipping themselves with weaponry and defenses, disguising themselves, adapting to the situation (or to the enviroment) at hand, and just keeping their tactics and antics varied in order to take you down (or make things harder than they should be).
Took a Level in Jerkass: E. Gadd spends a disproportionate amount of time making backhanded comments about Luigi's fearful nature and skill as a ghost hunter. One time he even compliments Luigi and says that he "may yet" become as famous as his brother... which he punctuates with a small chuckle, indicating that he was being sarcastic.
Unexpected Gameplay Change: The Scornful/Shrewd Possessor boss has you man a bomb-launching sled to blow up its giant ice face first-person style. You use similar machines twice before in the game- once earlier in the level to shoot burning charcoal, the other back in the second level as an optional way to get money and a Gem- but it can still be jarring (especially since it requires more precision and you only have a limited amount of time before the sled overheats).
Unwinnable by Mistake: The Thrill Tower/ScareScraper if a necessary key fails to spawn. There's also the story from this article's comments of someone who managed to quit between the Tough Possessor and final battle and find themselves locked out of the final boss and ending as a result.
The Very Definitely Final Dungeon: Treacherous Mansion. It's a huge castle-like structure suspended on a tiny piece of land above a gigantic ravine/waterfall, which also happens to be a museum based on the earlier levels in the game. And it has things like a pirate ship sticking out the side and part of a tree sticking out the roof for no real reason. The place could probably even pass as a Legend of Zelda final dungeon...
Weaksauce Weakness: During part of the Final Battle, King Boo has a weakness that Boos tend to have in Mario games: if Luigi looks at him directly in the face, he cannot attack Luigi or even move. This weakness is part of the strategy needed to defeat him (see Hoist by His Own Petard above.)
What Happened to the Mouse?: King Boo is not seen again after being sucked into the Poltergust 5000. He's not in the vault, there's no cutscene showing him being pumped out, he's not put in a painting... his crown's jewel also gets an unknown fate. Luigi picks it up and pockets it after the battle, but we never see him take it out nor does it count for any money.
When All You Have Is a Hammer: Much like the first game, Luigi uses only two weapons to fight monsters the entire game: A flashlight to stun ghosts (which is a lot more effective than the one in the first game) and the Poltergust 5000 (an upgraded version of the model he used in the first game; he does upgrade this several times during the course of this game too).
Wolf Pack Boss: The Three Sisters; technically a Mini-Boss, but it's three individual enemies at once. There are a few other battles that could be considered Mini-Boss fights which have more than one enemy, but in the other cases the ghosts involved become common enemies afterwards.
Zerg Rush: The game likes to simply throw a large number of Greenies at you in a small room, which can cause you quite a bit of difficulty if they get on top of you. Doubly so if they're equipped.
The Overset Possessor's fight turns into this near the end.
This is the whole point of mission E-4, when a paranormal portal opens in the mansion, releasing a large number of ghosts. Luigi must quickly capture them before the dimension itself collapses, and the level culminates with an absurd amount of ghosts fighting Luigi at once.