For context: one of my NPCs is an artificer whose "thing" is storing curses in gems - people bring him cursed items or people, and he then stores the curse in a gem.

I am planning on the players getting a handful of these gems - there will be an entire room full of them, and they are bound to be a little light-fingered with them as soon as they get the chance!

My plan is for them to function similarly to Magic Stone, except that they inflict weird and unusual curses on the targets instead of just damage!

As the artificers shop is open to all, he has a huge range of curses that have been stored - anything from the smoke from a fire always blowing towards you no matter where you sit (we've all had that curse from time to time eh?) to taking 15d10 psychic damage and, if they survive, transcending and becoming aware of their role as a fictional character in a tabletop roleplaying game!

In between we have all sorts - becoming aquatic, catching fire, transforming into a random object, I've got nearly 200 of them. But, I need more! I need 300!

So, please can you give me some wierd and unusual curses! If you know any from mythology (already got snake-hair and medusa eyes as one of them) that could make cool references I'll definitely be interested! Also weird ones (I've got "takes 1d6 slashing damage and their nose falls off as one already!) and decidedly fantastical and magical effects would be awesome!

Thanks!

The Curse of Tongues - The inflicted PC or NPC does not have control of the language they speak. When they try to talk they must roll a d20 and on each result the words they say come out in the language rolled.

1 - Common
2 - Dwarven
3 - Gnomish
4 - Draconic
5 - Elvish
6 - Halfling
7 - Thieves Cant
8 - Druidic
9 - Orcish
10 - Halfling
11 - Goblinoid
12 - Abyssal
13 - Undercommon
14 - Infernal
15 - Celestial
16 - Common
17 - Deep Speech
18 - Sylan
19 - Dwarven
20 - Gnomish

The PC can make a WIS saving throw to attempt to speak again but in the tongue they intended this time. The condition/curse may be resolved either with remove curse, or rolling a language that the PC speaks already.

In one game my wife DM'd each player had a minor curse. One of the characters was unable to see horses. They could see everything else just fine, but all horses were invisible. 

• Their boogers transform into bats.
• A cursed person can always see a duck. At all times, there is a duck within sight, and this has made them very paranoid of ducks. 
• They can only see in black in white. Or they and anything they hold or carry becomes black in white.
• If they touch a gourd, it becomes a vampire if it is left outdoors at midnight. (sort of based on mythology.)
• They can only see out of the bottoms of their feet.
• They become a werelawyer.
• They forget how to breathe. They begin to suffocate, and must roll intelligence checks to see if they can remember how to do it correctly.
• Whenever they sneeze into a tissue, the snot randomly teleports somewhere within thirty feet of them, in someone's hair, pocket, shoe, soup, etc.
• Whenever an ox sees them, it drops dead.
• Whenever they sleep, the world acts like they are dead. They stink like the dead, vultures try to eat them, they turn pale, they don't appear to be breathing and no pulse can be detected.
• They can only speak in rhyme.
• Their hands become talons. Now they cannot use them to wield weapons, write, or do anything requiring hands in that way, but they are useful weapons.
• Their hands and feet switch places.
• Other people keep referring to them in the past tense, and have trouble remembering they still exist.
• They can see a floating hourglass above anyone they see. The sand slowly drains away, and when it does, the person they see sneezes. Or maybe they die.
• Their reflection doesn't appear in a mirror. 
• If they stare at anything, or anybody, for too long, they begin to smoke, and then set on fire.
• All paper disintegrates at their touch.

You can steal some from pathfinder 2e they have spells and RP curses free on their wiki.  You will need to adjust DCs  to be more level appropriate but there's some interesting ones in there.

Some other ideas from dnd spells and monsters. The general principle is to make them not too punishing by making them only apply in some situations with certain triggers 

• Cockatrice has temporary petrified you can just run that or have it trigger in certain circumstances. Like getting petrified when ever you are kissed. 
• hex and bane.  Bad luck on checks can always be entertaining and you can limit them to any circumstance you like. 
• contagion There's some interesting diseases here that can act as curses
• feeblemind is pretty nasty but again temporarily triggering it in certain circumstances can be fun. For example when ever you try to speak to a noble. 
• geas this one is fun you can come up with a bunch of commands
• aboleth the aboleth's mucous cloud forces some one to be aquatic 
• wild magic surges and it's effects can be entertaining either pick one or roll the table
• Accidentally casting a spell like command, compelled duel or friends could be entertaining. Having it triggered by certain words or actions.
• shield of missile attraction attracts ranged attacks towards you
• the charmed prevents attacking and so charming them to certain creatures as a kind of love spell works well. 
• Otto's Irresistible Dance makes people dance so triggering that sometimes can be interesting 

Curses from myths 

Common curses in myths are often just that they invite misfortune in the form of attracting evil people, encouraging people to steal it or encouraging bad actions on behalf of the user. They also often turn people into monsters such as dragons, werewolves or animals. You can give them animal or monster traits as a curse.

• Blood of the Scab Mettler: When you bleed, your blood quickly scabs over, creating a natural bandage and/or splint. This grants you resistance to piercing and cutting damage - however, unless you can roll a Dex Save to keep the limb in question mobile, the joints scab over, making it useless. 
• When people speak to you, you hear the truth of their words in a whisper. However, you can only focus on one: You can either hear truth, or lie. Not both.
• You Heat Metal - as the spell. This damages you, if you let it. 
• Your voice become so annoying, over time it causes Psychic Damage. Anyone listening to you for longer than a minute starts suffering 1 point of Psychic Damage each round.
• Any text you write is comprehensible only to you.
• Your touch turns gold into lead.
• Anything you drink turns to herbal tea in your mouth. Scalding hot, so careful! Also, it's chamomile.

Your presence sours milk and spoils food.

Dogs are compelled to relieve themselves on your legs.

The sole of one of your shoes (not two, just one) is always smeared in cowpat.

Thankyou all for the responses!

I've added a bunch of them to the list! Still got 103 of them to make though, so keep them coming!

Your mother becomes a hamster, and your father starts to smell of elderberries.