And I Must Scream: The Wall of the Faithless, though the souls there do eventually cease to exist - it's just that the process is lengthy and extremely painful. Turns out to be the final resting place of former Token Evil Teammate, Bishop.
Animal Theme Naming: Kaelyn the Dove and her half-celestial siblings call themselves the Menagerie. The other members you meet are Efrem the Stag and Susah the Crow.
With high influence, Kaelyn may induct you into the Menagerie, after which you can add a similar moniker to your name. If you ask her what she thinks would be a good fit she suggests "the Wolf" after the telthor wolf you ate during your escape from Okku's barrow.
Blessed with Suck/Cursed with Awesome: The Spirit-Eater Curse, depending how you play it. While it's entirely up to you to decide whether it's either a horrible dog-raping curse or the most awesome ability ever, it's absolutely certain there's an NPC somewhere who will disagree with you and get violent about it.
Arguably, your situation is not great. Yes, you just beat an incredibly powerful avatar of the dark side of magic, but your close friends and followers may well be dead, and they're certainly incapable of helping you. The shard that has been inside your body for all your life has been removed (but not very well), you didn't get crushed to death at the end of NWN 2, but you are thousands of miles from home, trapped in a country full of beings who despise you. Oh yeah, and you're afflicted with a curse that has always killed all previous victims, turns you into an insane ravening husk along the way, and means that your soul automatically goes to the Wall of the Faithless when you die no matter what.
Body Motifs: Faces and masks (it is in the title). The spirit-eater curse is referred to sometimes as an entity in and of itself that happens to be "wearing" you as a mask, just as it's "worn" the faces of its many previous victims. A name for an important character in the backstory is The Faceless Man, and you can end the curse by restoring him to being Akachi - using a mask. Gann's beautiful face is something of a plot point, and his initial attitude masks deeper issues. Safiya's face is identical to that of her mother for a good reason. Kelemvor, new god of the dead, wears a very memorable mask. The woman who runs the Veil Theatre has a studio dedicated to creating masks for the plays, and even the theatre's name refers to a sort of mask. The city of Mulsantir has its own mask in its Shadow counterpart, where people often retreat to hide themselves. The witches who rule Rashemen are all masked. And a drinking game for every time somebody refers to masks, faces, or masks on faces, or faces beneath masks as a metaphor for anything is inadvisable unless one seeks liver failure.
To expand, if you play the Good Route, and suppress the thing, and only use it against the undead, then your craving will be far lower, and you will lose spirit points much, much more slowly, which is incredibly helpful during several very lengthy parts of the game with little to feed on. This can make for an easier time, but you can potentially deny yourself several powerful items and abilities.
Embracing the curse, and thus using it far more often results in a higher Craving, meaning you must feed more often,note to compare, if you suppress the craving, you will only lose 1 point per in game hour, if you feed constantly and have maximum craving, you will lose 6 points per in game hour; if you run out of spirit points, you die which makes the aforesaid lengthy parts much more difficult. Furthermore, to get the most out of each usage of an ability, you must time it so that you kill the enemy when they are below a certain threshold (below 25% health to restore the flat amount plus whatever life the enemy had left), otherwise it will restore a flat amount of Spirit Points, which if you've been embracing it, will probably be peanuts to what you need to stay alive. On the flip side, you can get and make some pretty damn powerful items and some cool powers.
Bragging Rights Reward: Akachi's Scythe can be combined with Myrkul's spirit essence to make an Infinity + 1 Scythe called Spiritual Evisceration. It'd be nice if you actually had something to use it on; instead you get it after you've probably already got your character at 30th level, designed for a weapon class unlikely to be scythes (which are rarely seen since Heroes Prefer Swords), and one short dungeon from the end of the game.
The Casanova: Gann. He banged so damn many girls that they locked him in prison.
Central Theme: Betrayal, duty, faith, love and redemption, and how all those things conflict or intertwine. Okku feels that he's trapped in an oath that he can't fulfil, and he'll never reconcile his duties to honor the man who trapped the curse and protect his clan. Kaelyn could not maintain her faith once she learned of the Wall of the Faithless, and her rebellion set her against her family, her god and her original purpose forever. Gann has no faith and refuses any duty, even when it seems he should be morally obligated in some way. Safiya lacks faith too, but feels bound by duty to protect the Captain which is revealed to be an extension of the deepest love, the purpose for which she was made. Also, ultimately, Akachi chose to betray his god rather than condemn his lover. You can resolve their conflicts in a number of ways. Or twist them. Except Kaelyn. Her rebellion will go on as long as she believes she's in the right. All you can change is how long it persists.
Cessation of Existence: The fate of anything consumed by the Spirit Eater. This is also the fate of those condemned to the Wall of the Faithless, but it takes time, and being slowly dissolved while paralysed isn't a whole bundle of fun.
Converting for Love: In one of the endings, either Gannayev or Safiya (both n/atheists) will swear themselves to Kelemvor so that they can stay with you in the City of Judgement.
Cute Monster Guy: Gannayev the Hagspawn. Lampshaded when he jokingly denies that he's a Hagspawn simply on the basis that he's way too pretty to be one. Gann looks so beautiful because his mother and father were genuinely in love when they conceived him.
Cutting Off the Branches: The expansion assumes a character that wasn't imported from the original campaign did notjoin the King of Shadows at the end.
The Dandy: Gann is entirely aware that he's probably the only attractive Hagspawn out there — a fact which he feels he must constantly broadcast to all the world.
Darker and Edgier: Mask of the Betrayer has a significantly darker and personal storyline than the vanilla game, and features themes rarely seen in video games, such as justice, original sin and faith.
Dark World: The Plane of Shadow is a dark reflection of the Prime Material Plane. There are no colours; the entire plane is monochrome. The terrain varies slightly in each plane, and the Plane of Shadows is populated by hostile undead called Shadows.
Dark Is Not Evil: The good ending for Kaelyn the Dove implies that Kaelyn becomes a fallen angel. Even so, a good majority, especially the souls on the Wall of the Faithless, still consider her a hero.
Did You Just Arm Wrestle An Iron Golem?: An NPC Berserker will offer to arm wrestle you, and is tough enough to beat a player transformed into an Iron Golem when he is at full power. To win, you need strength boosts on top of the transformation.
Dirty Mind-Reading: According to Gann, the prison warden of Mulsantir has more than a few dirty dreams to spare.
Gann: ...and old mother, do not think your mind has not laid down paths for me to stroll. Such thoughts in a woman your age – it would put even a farmer's fiery-loined daughter to shame.
Dissonant Serenity: Kaelyn always talks in a soft, motherly tone, which can be a bit disturbing when she's supposed to be angry, such as whenever she talks about the Wall or if you side with Araman in the endgame.
Dreaming the Truth: With dreams being a major theme of the series, it's only natural that several of the dreams you travel through through let you in on the backstory. Gann is helpful in this regard.
Dreaming of Times Gone By: Safiya confesses to having very twisted dreams of being trapped in the Wall of the Faithless - which she was back when she was part of the Founder.
Driven to Madness: Gulk'aush as a result of being forced to eat her lover alive, piece by piece.
Dysfunction Junction: Surprisingly averted... well, unless you have One of Many and regularly go out of your way to gain Influence with it, given the darker tone of this instalment. There's a bit of banter back and forth, and Gann certainly likes teasing Kaelyn from time to time, but the party feels much more cohesive and calm compared to the original gang - less a squabbling rabble and more a set of self-contained individuals.
Eldritch Abomination: Should you go for the evil ending, this is effectively what you become; a wandering eternal incarnation of emptiness devouring all in your path, a thing which has declared war on the planes by its very existence, capable of consuming even gods. One of Many is ecstatic; everyone else is horrified.
Eleventh Hour Super Power: The Spiritual Evisceration spell, which lets you instantly devour the soul of a target. But you only get it if you choose to devour Akachi, and you only get to use it in the very last battle against your companions when they attack you.
The Epic: If you believe Neverwinter Nights 2 was not this, Mask of the Betrayer is definitely qualified. The story spans over two countries and four planes of existence, making the Player Character meet and battle Gods of old, walk in dreams, committing extraordinary deeds with equally incredible companions, uncovering a mystery that affected millions since centuries, culminating in a crusade taking place in the land of the dead for the sake of their soul.
Eternal Love: Gann cheerfully points out in the ending where both of you remain in the City of Judgement that "eternal servitude" isn't such a bad deal once you think about it - after all, who else can brag about literally being together forever?
Evil Tastes Good: Given your curse is described as a "hunger", and given how often you can threaten other characters with it, several evil dialogue options take on this tone. And then there's One-of-Many.
Fallen Angel: Kaelyn the Dove can be considered one, being barred from entering Celestia. She becomes a real one in the ending as well.
Fatal Flaw: Kaelyn's obsession with destroying the Wall of the Faithless. There's one ending where it destroys her siblings and her spirit with them.
Flat Earth Atheist: Gann, even after meeting a god in person. This only becomes more interesting when you realize that he's a divine spellcaster — a type of magic which, by definition, requires belief in a higher power. The answer is he puts his faith in spirits.
Game-Breaking Bug: The initial version broke the "go to the swamp to retrieve the silver shard" quest early in the original campaign by causing a Plot Lock to fail to open.
Guide Dang It: The Golden Ending requires items you can only get by doing optional sidequests in optional areas with Gann in your party.
God's Hands Are Tied: Kelemvor would love to end the Spirit-Eater curse for you, but the entire pantheon would come down on him if he were to toss aside another god's judgement against his own follower. However, he is willing to abuse some loopholes to let you end it. The Wall of the Faithless, on the other hand, is there to stay for the same reason he can't end the curse himself, only more so.
Kelemvor: Even the gods are bound by laws, Kaelyn.
Golden Ending: Reassembling the Mask of the Betrayer lets you return the last fragments of Akachi's mind to him, enough to finally let his soul rest. This ends the Spirit Eater curse and lets you go off on your merry way, something all your companions (except One of Many) approve of. See Guide Dang It above though.
Good Is Not Nice: Kaelyn is genuinely heroic, but she tends to get... angry when the topic of the Wall comes up.
Good Versus Good: The crusade involves celestials fighting paladins to the death. Or even paladin versus paladin, if the player is one.
Go Out with a Smile: According to Gulk'aush, Gann's father kept his smile, even as he was flayed alive.
Genius Loci: In the Ashenwood, there are two. One is a spiritual entity with higher reasoning, personifying the wood, that defends both itself and all within it. The other, actually called a "Genius Loci", is a feral, enraged, collective instinct that arose when the other spirit was attacked viciously and left too weak to protect the wood.
If you're male and had romanced Elanee, Ammon Jerro reveals that she took a piece of the King of Shadows' Collapsing Lair that would have struck you.
Casavir is said to have died at the end of the original game while holding up the collapsing ceiling of the Shadow King's lair to buy time for the rest of the group to escape. The truth of his demise is in question, as someone very similar to him show up in Storm of Zehir.
I'm a Humanitarian: The uthraki, shape-shifting apes who feed on human flesh and think of spirit-eating as a gift. You'll meet a family of them, the Hill Tribe, who will either teach you to devour the souls of humanoid characters (rather than just wraiths, ghosts, undead or elementals) or attack you, depending on whether you spared Okku, and evil PCs help them catch victims by leading certain NPCs to their den. During the Slumbering Coven quest, you can offer one of your companions or a mute slave child to some other uthraki if sufficiently evil.
Insult Backfire: Insulting Gann often increases your influence with him - though it has to be a witty one. He enjoys a good verbal spar.
Intellectual Animal: Okku is the spirit of a bear, and often offers advice both from his perspective as one and from his perspective as a protector of the land.
Journey to the Center of the Mind: The last battle in the game takes place within your own soul, the atmosphere of which is different depending on your alignment. There, you and Akachi have one last throw down to determine who gets control.
Killer Rabbit: There's a spirit badger outside the Ice Troll Lodge in Mulsantir that hates you, but can't harm you, partly because of binding spells but also because it's only about as large as your foot. Should you massacre everyone in the Lodge, your last opponent will be the badger - now the size of Okku, with stats pumped through the roof, and entirely capable of ripping huge chunks out of your health. It is very likely to avenge its fallen masters if you don't cheat.
Last Villain Stand: Provided you proceed with the invasion of the Fugue Plane instead of defending against said invasion, Araman decides to oppose you, serving as the last villain of that segment.
Love Makes You Evil: Indeed it can, and indeed it has. It's one of the main themes of the game, central to the reason the PC is in this mess at all, and Myrkul actually says it in so many words, with all the gleeful and malicious irony he can muster. Only love could be so cruel. However, the trope is also inverted and played with if the player goes snooping through enough of the incidental story.
MacGuffin Title: The Mask of the Betrayer actually makes an appearance in the final battle if you manage to collect all the mask fragments. It's even useful in protecting you from Akachi's soul-draining abilities.
The Magocracy: Rashemen is ruled by masked witches - and witches only. No men. The older they are, the greater their authority. Minus the gender restriction, Thaymount Academy (and Red Wizard society in general) works this way too, but with rather more backstabbing.
Merger of Souls: The Academy of Shapers and Binders has a wizard who can fuse souls, and bound his own soul into a clay golem to do it more safely. A sidequest on the same level requires you to trade a soul to two pit fiends. Unfortunately, since they're unwilling to hand over what you request, they won't agree on what sort of soul they should have; in fact each gives mutually exclusive requirements. The solution ends up being to have the aforementioned wizard fuse two completely opposite souls together. They get really annoyed with you for finding that loophole, but they have to honor the agreement.
Mundane Utility: According to Gannayev, the best use for travelling through dreams is getting laid.
Narrator All Along: Kelemvor, God of the Dead, is revealed to be the one narrating your story. Since you don't meet him until you're minutes away from the game's end, you're unlikely to recognise his voice until then.
Nature Spirit: Quite a few, but Okku most notably. The existence of these spirits, "telthor" and the local worship of them is arguably Rashemen's hat.
No Blood Ties: Hags always abandon their male children, as they have no use for them.
It's a slight implication at best; whether you try to purge it with eternal rest or not, One of Many escapes in a weakened state; if you try to exorcize it with Eternal Rest, it merely thanks the Soul Eater for purging it of its weakest spirits.
Not in This for Your Revolution: The expansion pack is praised for giving a motive that is believable for all characters — saving yourself from a curse that is slowly killing you — over the "save the world" that the original game forced the players into. So even if the player character has no reason to stop what has been plaguing the lands for decades, they still have a reason to finish the main quest.
You can choose to take it a step or three further. You can turn against the Crusade most of the party wants you to join, kill the Founder out of vengeance for roping you into this mess, abandon or kill your party and - while the heroic option is to stay on the Fugue Plane for eternity to contain the spirit eater deep within the recesses of your soul (or with a little extra work, end it forever) - you can also throw the curse out of your soul and send it on its merry way to a new host. You then return to your friends and the Keep from the original campaign as if none of it had ever happened.
Optional Party Member: One of Many is an odd example, as you can get either him or Okku, depending on whether you consume Okku. Similarly, Araman can be obtained if if you side against the Third Crusade in place of Kaelyn (who will attack you if you meet the conditions for him).
Peek-a-Bangs: Gannayev, possibly symbolic of his deep-seated and carefully hidden fear of showing people who he really is.
Plot Hole/Writers Cannot Do Math: Part of Myrkul's plan in creating the Spirit-Eater Curse was to ensure his immortality by abusing the Forgotten Realms'Gods Need Prayer Badly rule (i.e. as long as there's a Spirit-Eater, there's always going to be someone who fears it and fears the one who created it, thus he can't truly die). Problem is, the Spirit-Eater has been around for centuries, but the Time of Troubles, after which Gods Need Prayer Badly was established by the Overgod Ao (and incidentally, during which Myrkul was killed and replaced by Cyric as god of the dead), took place in 1358, and the game takes place in 1374. Perhaps Myrkul was just really forward-thinking.
Ragtag Bunch of Misfits: Consisting of you (already a Walking Disaster Area linked to the Silver Sword of Gith who then gets cursed to become a soul-eating abomination), a somewhat Machiavellian wizard from an organisation of similar but much nastier wizards, a Hagspawn casanova who uses his dreamwalking powers to give the local ladies very pleasant dreams, an exiled half-angel rebelling against the gods themselves, and either another soul-eating abomination created from the fused souls of dozens of cremated individuals or a giant talking rainbow spirit bear god.
Sequence Breaking: Getting Gann's influence high enough before the end of Act I will tip you off about the spirit eater curse before you're supposed to know about it.
Soul Jar: Several - especially at the Academy of Shapers and Binders, which contains a library specifically for soul housings.
So Beautiful, It's a Curse: Gann is apparently so damn pretty that they had to throw him in jail to keep him from banging every girl in Rashemen.
The amazing part is, they actually pull the trope off without making it seem utterly ridiculous; he's a pretty hagspawn, so none of the local humans trust him worth a damn and the only reason they don't kill him is out of fear that he'd overpower them and take their daughters anyway, and he's a pretty hagspawn, so all of the hags find him legitimately abhorrent and not actually "beautiful" at all. Even his mother takes a while to come around, and by the time she did, it didn't do either of them much good.
Sociopathic Hero: One of Many, a terrifying soul-eating spiritual construct that craves power and revels in suffering. If it approves of something you've done, you can be assured that whatever you just did was an act of selfishness, cruelty or both.
Speaking Simlish: One Of Many is a dark twist. It speaks with a "call of the dead" that any mortal creature can understand.
Stupid Sexy Flanders: A male PC with a high enough Charisma stat can catch Gann in one of these moments when they first meet, likely an artifact from when Gann was going to be bisexual.
Star-Crossed Lovers: Akachi and the Founder. A devoted disciple of Myrkul and a Faithless...and that was only the start of their problems.
Status Quo Is God: For all the epic changes the campaign allows you to make, you can still play in such a way as to have essentially nothing change when you end it. You can reject or kill all your companions, put down the Crusade, eject the spirit eater to resume its course, and, if your character is an import from the original campaign, return to Crossroad Keep and reunite with your old friends.
Uneven Hybrid: MotB adds genasi, humans with a touch of elemental blood, as playable races.
Video Game Cruelty Potential: Obsidian hasn't lost its touch. Playing to abuse the power of the curse is only the start. Feel free to trick innocent people into being trapped and devoured by uthraki (flesh-eating shape-shifters), such a family of merchants with two children, a mute pre-adolescent boy, a pair of eager young warriors and a mentally ill farmer's daughter. Then there's creating another evil soul-eating abomination to hang out with by having hundreds of dead, deranged spirits inhabit the shell of a spirit you devoured. Use it to kill and devour the spirits of people whose abilities or memories will be useful to you. Psychologically abuse and torment everyone you meet for laughs! Betray your companions and and devour their souls to create a nifty stat-boosting amulet! Skin a person alive! Take your revenge on the one who gave you to the curse by consuming their spirit, which is in context even more horrible than it sounds! Defend against the Crusade, kill Kaelyn's siblings, get her grandfather-solar to come and try to stop you, kill him, and leave Kaelyn mortally wounded but alive for demons to collect, in utter anguish. Then put the cherry on the sundae of evil and manipulate the curse to turn yourself into an abomination against all that lives that devours whole nations and even gods who cross your path.
Villains Never Lie: Myrkul. The player character can even lampshade it to Kaelyn. Later subverted when Kelemvor reveals that though he wasn't lying to her, he was lying to you and to the Founder.
Warrior Heaven: If you choose to bind Akachi to your soul, Kelemvor is more than willing to reward your sacrifice by at least making the afterlife comfortable and exciting for you, and you spend all of eternity kicking ass and taking names in the Fugue Plane with either Gannayev or Safiya as the other half of your eternal Battle Couple.
What the Hell, Hero?: In both of the standard endings, at least one member of your party will be unhappy with your choice. Binding your soul to Akachi's will anger Kaelyn, as it means you've sworn yourself to protect the very thing she seeks to destroy, and the One of Many mocks you for choosing an eternity in the City of Judgement. If you free yourself from the curse but not end it, however, Safiya will be angry that you've let Akachi continue to suffer, and Okku will be mad that you've ditched your chance to end the curse for good for your own survival. And then there's the Bad End, where everyone (save the One of Many) will be against you for committing such a purely selfish, evil act and becoming a god-forsaken abomination.
You Are Worth Hell: If you choose to stay on the Fugue Plane in order to bind the spirit eater, your love interest will go as far as pledging their soul to the God of the Dead so that you won't have to be all alone.