So like... M'aiq the Liar?

The shopkeeper-with-wanderlust who supplies your party during the first area of the game, and then joins your party once you move onto the next area.

You know, I've never actually played WoW, which is odd, considering I've played practically every big-name MMORPG out there.

Hrm... The once-a-year event NPC and her drider friend who hangs out in the town square for two weeks during the Halloween season; you can get event currency from most in-game activities and trade them to her for various goodies and buffs.

:D Ohhhhhh! I see it yeahh, *has played WoW* But with like, a Dragonhawk.
But also...

the one-time enemy in a RPG that turns out to just be the quest character who later is visted again and gives the player something useful in exchange for a rare item they really want a lot of. x}

A quest giving NPC who shows up in the strangest locations, with no reason given as to how she got there before the main character(s). May or may not know all sorts of random trivia about the location that incidentally is helpful for a puzzle nearby

An observer in shadows that changes peoples knowledge level about you when you are cought by their sight?

Fallen angel with ambiguous morals that leave you questioning whether they can really be trusted

A spider boss with minions that are unexpectedly evil duckies instead of spiders. x}

The lost scion of Atlantis an ancient underwater kingdom, who you meet... halfway around the world, as an amnesiac. Seems kind of harmless at first but then she summons a pelagic behemoth in battle and the enemy drops their weapons and runs away screaming.

The bird trainer that gives you the ability and items you need to capture and tame every bird you can encounter yourself, in exchange for a bird/hunting related side quest of course.

you are the death fish monster. you try to kill the party just before the save point. lol

The NPC that once appeared for what was supposedly a one-time event, until the dev team caved in to the requests of the player base and made it an annual thing. They hang around the event area, trading kill tokens for really weird shit.

AN NPC THAT SELLS MOUNTS. THEY'RE A BRILLIANT BEASTMASTER, TOO.

havent played but
 

the protagonist from Don't Starve

end of stage villain ready to wreck of your shit unless you come to play overpowered

An easter egg character who's generally an NPC merchant and sells you weird shit like really niche potions. You can recruit them into your party via cheat codes, but they'll jokingly scold you for using cheat codes.

your own character but only if you pay for the DLC wardrobe expansion that's like, 80 dollars
one hit kills only

The fanatical wizard of rainbow unicorns you meet in order to obtain their special gem or key or piece of an amulet. :]

I would pay $80 for a DLC wardrobe expansion. Maybe.

A shopkeep who peddles arcane and supernatural wares. She lives in a seaside cavern and sends you messages with special offers via seagull.

>:D I'd LOVE to have Seagull mail! xD

That one boss that you JUST! CAN'T! BEAT! Because he's so tricky and has that one attack that does MASSIVE damage if you don't avoid it in time! x'D

Honestly... I am reminded of Raleigh from Sly Cooper lol.
So... The first "boss" of the game.

<x} I had to look him up bc I haven't played Sly Cooper since I was 6 or 7. (I can see the color scheme matches up almost perfectly! o_o;)

One of the many elegant, elemental, wise characters you meet and they give you a new power of some sort, or a treasure to unite together with the other elemental beings. :] This one being like, a beautiful leafy earth sage that lives in the forest with wooden horns.

A companion in a cyberpunk game that you first assume to be an inconsequential NPC, until they later appear in avatar form while you're trapped in cyberspace, and help you remember who you are.

During their companion quest, you slowly uncover their secret persona as one of the elite deckers/hackers who undermine government efforts to eliminate "undesirables" from inner city slums, and help them out of a bind when soured past relations catch up with them.

The first of the final bosses on a perilous climb up a mountain in a horror/fantasy rpg. An angered soul of a lost city, and keeper of the graves of the machines that used to rule the mountain mines, that stands in the way of the hero!
o.o

probably can also only be defeated by torches or something.

A disillusioned dancer who you find sprawled in the snow in front of your party's keep one morning. Getting them indoors is a bit tricky, but becomes easier after the mage figures out that moving half-incorporeal bodies is significantly easier with the use of magic.

Halfway through the main storyline, your bard is revealed as a spy for the main antagonist, and their betrayal leaves a gaping hole in your party lineup. If you've completed the first part of Mer's companion quest, you can take them along with you on your travels, which allows you to eventually encounter the trigger for the second part of the quest, after which her bardic abilities are significantly boosted.

The main protagonist of a futuristic fantasy game, OR
a character in a futuristic fantasy game which sides with the protagonist and becomes the speedy tactician of the party. They've got little strength and defense but they more than make up for it with their speed, precision, and brilliant boosts in ability points, making them very useful for evading danger, strategic boss battles, and is the character with the most weapon choices.

They've also got a cool ass cyborg backstory likely involving a main antagonist or their tech corporation.

Mage in back of the group

The sultry side character that likes to tease but also gives good advice to the main character. Probably has a hidden secret that the main character is tryingt to figure out.