Amazon Brigade: As with the OC, it's possible to establish an all-female party using Lastri, Inshula, Soraevora, Chir and Belueth, and any combination of player characters.
Apocalyptic Log: The former owner(s) of the tower Tempest's Fury in Samarach were experimenting on a djinn. (No points for guessing what happened.) There's a journal in one of the rooms; the second-to-last entry is, "I'm certain the wards on my room can keep him out." The last entry reads, "I was wrong about the wards."
Can't Catch Up: Unlike the OC and Mask of The Betrayer, there's no Leaked Experience for companions that aren't part of your party. You can however take them to the adventurers' guildmaster who will bring them up to your level. The fee depends on the gap between their level and yours.
Canon Immigrant: Zehir was introduced in Storm of Zehir, then made canon as a subservient deity of Bane by the 4E Forgotten Realms Campaign Guide.
Several companions were mentioned in previous campaigns — Septimund is the Doomguide whom Nya from Port Llast fell in love with, while Finch, a bard known for losing his best hats, finally shows up. Ribsmasher also appeared in the Original Campaign.
Crossover: One sidequest in Neverwinter features a quest giver who traveled to the Realms from the city of Sigil in the Planescape setting. It helps that many of the people who worked on NWN2 were also part of the Planescape: Torment team.
Doomed by Canon: The events you see in the scrying pool is the start of a calamity that will shatter this version of the Forgotten Realms setting. The whole area around Neverwinter will be destroyed by the Spellplague in a few years.
Easter Egg: One possible encounter is a man trapped in a beartrap. You can free him or kill him (standard stuff), but if you have a cleric of an evil deity, you can sacrifice him, with unique dialogue for each deity. Annie Carlson notes that she found writing this to be fun.
Hellfire: Storm of Zehir adds on the Hellfire Warlock class, which simply lives off this trope.
Hero of Another Story: While the Knight-Captain was busy dealing with Akachi, the SoZ protagonist was busy saving the world from an evil god.
Interactive Narrator: After the ending narration you can yell at Volo until he gives you another version (allowing you to see every variation of the ending), and he also exists in the story himself.
Lighter and Softer: Zehir swings strongly back toward the "Slayers-esque" kind of D&D play similar to the NWN2 original campaign, after how deep and dark MotB was. Granted, the guys at Obsidian were upfront about it from the start this time and deliberately set out to make a game that was, at times, aggressively silly. And occasionally awesome.
Opening Narration: Volo explains over a brief montage why the party is traveling to Samarach with him, then tells of the storm that shipwrecked everybody.
Our Goblins Are Different: Chult's batiri are jungle goblins that serve the role of primitive native tribes. They use stone tools and weapons, paint their bodies, and eat people.
The Overworld: The game got one here. Previously the game had you fast travel between locations.
Overworld Not to Scale: Random encounters and the party were modeled very much out of scale with the map and the locations, though at the start of an encounter the action would shift to a smaller map of correct scale.
Rage Against the Author: The story is as told by Volo, and if you don't like the ending you can yell at him (or bluff him) until he changes how things went.
Random Encounters: Many, many varieties on the overworld map, ranging from run-of-the-mill monster battles to item-gathering opportunities to a few scripted encounters.
Reptiles Are Abhorrent: The enemy in this game, both to the xenophobic Samarachans and to the player, are the snakelike yuan-ti. Not played completely straight, seeing as how the player can create a yuan-ti and make them non-evil.
Oddly, local Yuan-ti hunters won't notice unless you're dumb enough to explain it, because the player-usable yuan-ti form, the "pureblood," is meant to be able to blend in with standard humanoids.
Stereotype Flip: Besides the various stereotypes flipped by your cohorts (see the character sheet), Neverwinter has a Red Wizard enclave whose head hangs a lampshade on this. He's a member of a Red Wizard faction that thinks making lots of money selling magic items is a better use of their time than trying to take over the world.
Character creation in SoZ borrows a couple of "heritage feats" from the Planar Handbook. Non-lawful characters can take "Fey Heritage" at 1st Level, giving them a touch of fairy blood, while non-good characters can take "Fiendish Heritage". Turns into Heinz Hybrid if you take both and/or put them on a half-elf, half-orc, or planetouched.
One sidequest has the party investigating the theft of the Hammer of Ironfist by a group of fire genasi bards. Another has a fire genasi from Sigil who is gathering items for a museum there.
Tightrope Walking: Discussed in a dialogue option. When investigating the wreck of the trade ship Vigilant, if your party contains a rogue they can observe that they've stood on ropes thinner than the one that snapped in the storm. It broke because it had been partly cut through by a saboteur.