Affably Evil: Mephasm, an Always Lawful Evil Devil who is soft-spoken, helpful to the player, and not even interested in making you sell your soul to him. He even responds to Ammon Jerro's slaying of his own granddaughter Shandra with seemingly genuine regret and no malice at all. On the side, he implies that he is Neeshka's devilish grandfather.
You can create a balanced all-female team pretty early using Qara, Neeshka, Elanee, and a female Knight-Captain built as a tank. Act II adds Shandra Jerro and Zhjaeve to the mix.
Even easier in Storm of Zehir, which lets you handcraft your own party.
Androcles' Lion: During your investigation into the Ember massacre, you'll find a giant intelligent spider named Kistrel in a cave. If you don't kill it, it proves quite benign, and later shows up in Crossroad Keep's basement and knits you a nifty cloak.
Anti-Villain: The gnome sisters, Mirri and Jilla. They were infected with lycanthropy by a werewolf. They exiled themselves in a cave to avoid hurting anyone. They hunt forest animals for food or eat their insect collection when they can't find anything to eat. However, when someone enter their lair, the scent of flesh drives them crazy and they can no longer control their murderous hunger.
The OC limits you to three party members for Act I, three party members plus Shandra for Act II, and raises it to four after she gets killed.
This gets even more egregious in Mask of the Betrayer. You get a maximum of four companions and a party limit of three, which means you always have to leave one behind. This is unusual since the party limit for the last half of NWN2 is four.
Storm of Zehir limits you to four party members, counting the party leader, and one cohort (raised to two cohorts if one of the party members takes the "Leadership" feat).
Artificial Stupidity: Here's a few examples: tanks will charge past several mooks in order to attack a random one and will often leave a mook near-dead and attack another one instead of killing them first. Spellcasters will bombard enemies regardless of threat level and numbers and clerics or druids will buff up your party even when not necessary. You're better off playing 100% manually, but believe it or not you're also better off than you were in the first Neverwinter Nights: at least your companions won't randomly go charging off to attack enemies on the other goddamn side of the map.
Another fine example of Artificial Stupidity is the tendency of your own party members to attack Elanee the druid while she's transformed into her animal form, after they've run out of other enemies to attack. Resting won't stop this, since your party members are still in combat, which prevents Rest from working.
Ass in Ambassador: Both Torio Claven, Luskan ambassador and Garius' underling, and her replacement, Sydney Natale, take this trope to new heights. At least Torio can be reformed by the end of the game.
Attack of the Town Festival: Subverted. West Harbor's Harvest Festival goes off without a hitch. The githyanki attack that kicks off the plot happens after midnight that night.
Bag of Holding: The original version. Hey, it's D&D; what did you expect?
Black Comedy: You can choose "Sociopath" as a male voice. When leading, he will sometimes say: "Follow me... I have such sights to show you." It's also possible for him to start laughing hysterically when he realizes he's about to die.
One of the poorer examples of the trope. The feat only allows you to purchase additional magic items from a few merchants. By the time you get access to these merchants, you should easily be able to craft much better items for virtually nothing.
Hey, Amie, don't you think it might be a bad idea to piss off a wizard that's giving your master a hard time?
In one notable late-game encounter, you run into a group of bandits who intend to kill you for your magic items and the Luskan bounty on your head. You can remind them that you've already left thousands of bodies behind you. If you pass your Intimidate roll, some of them run off, while the rest charge into pointy death at the Knight Captain's hands.
The intimidate skill can actually be used numerous times, another standout is intimidating Jalboun into ditching his mercenary orders to attack you.
The Butcher: You get the "Butcher of Ember" background feat after Luskan frames you for said massacre.
Central Theme: The nature of heroes. Basically everybody was the Hero of Another Story, but either stalled out and failed to rise to greatness or fell to evil one way or another. Even the Big Bad wants nothing but to defend his homeland, even after they turned on him.
Changing Clothes Is a Free Action: This is one of the breaks from the pen-and-paper rules. Changing clothes happens instantly; the only real restriction is that you can't do it during combat.
Chekhov's Armory: The guns hang in bunches. There's the other old ruins outside of town, the fact that the Gith seem to think a shard's in town when you're around, the talk of Cormick and Lorne...
Clear My Name: The trial arc has Neverwinter's longtime rival Luskan accusing you (at the behest of Black Garius) of massacring an entire village. Nobody in Neverwinter actually believes them, but the law must be upheld so you're charged with murder and put on trial.
Character’s health status goes like this: Green = uninjured, Yellow = barely injured, Orange = injured, Red = near dead.
Challenge Rating is also color coded: White = effortless, Green = easy, Blue = moderate, Yellow = challenging, Orange = very difficult, Red = overpowering, Purple = impossible.
Comic-Book Time: The last Shadow War happened when the future Knight Commander was an infant. So depending on race that can mean eighteen years ago or a century. They get around this by the only witnesses you talk to being elves and very old humans, and at one point there's confusion how many generations removed a participant was from a modern character.
The game frequently references that Neverwinter is still recovering from the plague and the war with Luskan that the city suffered from in the previous game. Also, Deekin, the most memorable companion from the two expansion packs Shadows of Undrentide and Hordes of the Underdark, appears as a shopkeeper and references events from both expansions — albeit in a way that only those familiar with them will have any idea what he's talking about.
Also, a reference outside the plot but within their universe: at one point, Zhjaeve actually talks about Dak'kon, who apparently is an almost legendary figure.
Storm of Zehir features glimpses at events that should be very familiar to those who know what happened in the Realms between 3.5 and 4th edition D&D rules. You see a scrying vision of another plane, where a beautiful woman lies dead while a hawk-headed man stands over her. You also get to meet an illithid who apparently read the mind of a seer and saw the murder of Mystra. He is Driven Mad by the Revelation.
Cool Sword: Make that Cool Swords, plural (and you can even design your own). This is Dungeons & Dragons, so the trope is to be expected, but the Silver Sword of Gith takes the cake. See the Trope Page.
Canonically, Qara dies no matter what she ends up doing in the ending (obviously, you kill her if she betrays you; if not, she gets her head crushed by a rock) while Sand is implied to survive if he's on your side.
This will also happen to Casavir and/or Elanee, regardless or whether you romanced them or not.
Mask of the Betrayer assumes (not unreasonably) that the Knight-Captain defeated the King of Shadows. Storm of Zehir in turn seems to indicate (by One of Many appearing in a random encounter) that the Knight-Captain turned evil in the Unapproachable East.
Although if you keep in mind that Storm of Zehir takes place while the Knight-Captain hasn't returned from Rashemen yet, it is possible that (s)he simply couldn't stop the spirit-eater hunger from killing Okku, created One of Many without knowing the consequences and banished it afterwards.
Averted in the original campaign and Mask of the Betrayer. Party members who lose all their hitpoints suffer a Non-Lethal K.O. and recover at the end of the fight. Three friendly characters suffer Plotline Death and can't be resurrected.
Played straight in Storm of Zehir. Downed party members will bleed out and die if left unattended, but reviving them is as easy as casting a spell, going to a Temple of Waukeen to have it done for you, or using a Coin of Life (a consumable item that casts resurrection).
Determinator: Ammon Jerro. It takes some serious will to do everything he does, while refusing to excuse any step of it as being even a sliver righteous. He's a monster, he knows it, and to stop the threat that would unmake the world, he has damned himself for eternity without a moment's regret... Well, until he realizes he's gone too far being The Determinator, and his granddaughter dies because of it.
Determined Homesteader: A famed trait among the citizens of West Harbor. No matter how many times their village gets utterly destroyed, they will return and rebuild.
It's also stated that the smarter bandit and lizard clans in the area know not to mess with the village - They fight back.
Khelgar Ironfist: Just to make sure my eyes aren’t lying to me –- a huge suit of armor did smash through here, attack the githyanki –- and us –- then we drove it back to the portal? Because if my drinking is catching up to me, then I'm stopping right now.
Doomed Hometown: West Harbor, although this is played with. An attack on the town starts the story as per tradition, but the town and most of its inhabitants actually survives (your initial goal is actually to bait the attackers away) and can be visited later. Then it really is destroyed by a completely different enemy at the end of Act 2.
You can visit the village again during the 2nd expansion, Storm of Zehir. Guess what? It is now under siege by dragons. West Harbor is the Butt-Monkey of the Sword Coast, seriously.
Dysfunction Junction: All of the party members have some sort of severe mental baggage or messed-up past (if not both), all of the party members regularly bicker and annoy one another, and all of the romances are dark, strained, and doomed. This can mostly be laid at the feet of Chris Avellone, who has a severe aversion to straight-played romances.
Earn Your Title: You gain various history feats as you advance through the story. One of the best examples of this trope is "Master Orator", earned by completing your trial for the Ember massacre with such a thorough acquittal that the Luskans are completely trounced.
Feat text: Your considerable skill in the courtroom is the talk of Neverwinter's legal community. Local barristers will be studying the transcripts of your trial for years to come and comparing their performance against yours.
Grobnar:"Kalach-cha". "Kalach-cha". Well, it's not Gnomish, Elvish, Dwarvish, Orcish, Goblin, or Draconic — well, unless the 'k' is silent, but that would make it "gizzard stone" or the equivalent.
Enemy Mine: Casavir and/or a paladin Knight-Captain would probably (depending on the DM) not be allowed to work alongside evil teammates Bishop and Ammon Jerro in a pen-and-paper game. It could easily count as a violation of the paladin code of conduct and they'd lose their powers over it. Thankfully NWN2 paladins don't have that class feature or the game would be unwinnable.
Escaped from Hell: Ammon Jerro fought his way free of the Nine Hells and back to the Prime Material Plane after being transported there by breaking the Sword of Gith fighting the Big Bad.
Escort Mission: Sometimes NPCs being escorted can be told to wait or survive at 1 HP no matter what hits them, but when they aren't, it's fun.
Face–Heel Turn: Bishop, as well as some of your other non-Good party members, depending your influence over them.
Special mention goes to Sand and/or Qara, as it is literally impossible to keep one without the other turning. No matter how well you have treated her, how much you've agreed with her, or how much she likes you, if Qara's influence score is equal to or less than Sand's she will complain about being tired of being treated like a dangerous psychopath by people without any real power and decide to betray you and help destroy the world. If Sand's score is a single point below hers, the otherwise quite reasonable and intelligent wizard will suddenly conclude that the sorceress he's been working alongside for weeks is a bigger threat than the abomination that is literally in the process of exterminating all life on the planet, and join the bad guys simply because it means opposing her.
Fake Difficulty: How much easier would this game be if combat was coded competently, or even if your party members had half competent AI?
Not much. With fan made add-ons, the AI gets smarter... and so do the enemies. As buggy as the combat is, it's somewhat in your favor, given that you're generally outnumbered.
The most effective tactic in D&D 3.5 is to buff your party to the point they are almost untouchable and just beating everything down with your damage augmented weapons. The AI is almost completely irrelevant for this tactic since it is smart enough to attack the closest enemy.
Also Ammon Jerro. As the game points out, there's a reason that he and the King of Shadows get mistaken for each other.
Fantastic Legal Weirdness: A defense option in your murder trial in Act II is to use a boy with True Sight to cast doubt on eyewitness testimony that you led the massacre of a village (it was really Luskan soldiers under a magical illusion, which he saw through). Your opponent, Luskan ambassador Torio Claven, tries to counter by disputing the boy's ability, but he proves it by telling her about the medallion she has in her pocket.
Neeshka seems to be a regular victim of this to the point that the PC is labeled as the only person who has ever been nice to her at endgame if you have stable Relationship Values.
Deekin, as well, complains about how often he has to tell people he's not dangerous and means them no harm.
Also, kobolds hate gnomes. This leads to a funny moment when Deekin sings a song about butchering gnomes and Grobnar misses the point completely.
Khelgar starts out not liking Elanee and Neeshka because they're an elf and a tiefling respectively. Part of his Character Development allows you to prove to him that he's wrong.
The Knight-Captain can also go through this at different points through the game depending on what his or her race is. One example being in the arc where the Knight-Captain is accused of slaughtering the village of Ember, which has a guard in port llast who is willing to attack you brings up your race if you're part of one that has a dubious reputation (like the Drow) after you deny slaughtering Ember. Bevil notes that a tiefling Knight-Captain probably reminds people of the demons who tried to destroy West Harbor years ago. And a half-orc will be insulted by orc leader Logram Eyegouger, who claims their human blood makes them weak.
Fiery Redhead: Qara. In Mask of the Betrayer, the PC can describe her as "an impulsive red-headed mage girl with an anger management problem". She's also a sorcerer specialising in fire, so is a rather more literal example of the trope than most.
Carried over from the Baldur's Gate series, reducing a troll to 0 HP just makes it fall over. You have to hit it again with either acid or fire to get it to stop regenerating and die.
This in turn originates from the Dungeons and Dragons source material.
Subverted once in Mask of the Betrayer, in the crematorium of Myrkul's temple in Shadow Mulsantir. Probably because burning was used equally as a form of execution and torture as it was for getting rid of corpses (Myrkul was not a nice death god), the furnace room is infested with incorporeal undead. Luckily you can potentially learn a useful anti-undead power in that incident (or possibly turn them into the party member One of Many), so it's not all bad.
Flavor Text: Any equipment has his little story to tell.
Foregone Victory: Performance in the initial Ember trial is irrelevant, as you will still have to face Lorne in trial by combat.
Foreshadowing: Several drops and occurrences of "betrayal" appear in the Official Campaign, which leads to the expansion pack.
It's heavily implied that the reason Lorne betrayed Neverwinter and joined Garius was that he never got over his humiliating defeat to Cormick in a previous Harvest Cup, as well as his cowardice during the war in the first game, so he joined Garius in a bid to become stronger than ever.
Subverted with Bishop. He's got the perfect setup for one, but he's just responsible enough not to believe it.