Curse Imps - A different kind of way to inconvenience your players

Most Demons are far too important and powerful to bother with you. Their uncountable eternities are far too precious to be taken up with the likes of pesky little mortals who killed a cult of theirs in one of the inscrutable infinities of the creations Demons watch over. However, they would still get pissed off by it, and as long as it wasn't a particularly big or important cult, they would probably send a Curse-Imp or two to make your life just that bit more unpleasant.

Curse-Imps are invisible, dwelling in the ethereal mists between atoms and energies, much like ghosts, only altogether more petty and malicious. Their lot is to crouch on your shoulder, hang off your back, and mess with you. There are many types of Curse-Imp, and each will harass you in their own special way. They can't literally hurt you, but they can make your time in this world just a touch more miserable.

Getting rid of them is as simple as a small exorcism by a reasonably proficient cleric. Actually realising that it is a Curse-Imp is altogether less easy.

Here are a few:

Headsplitter Imps - That pain in your head, that feels like nails being driven into your temples that just started with no discernable source? Probably ethereal nails being driven into your ethereal temples. These ones perch on your head like a bird, a clutch of crooked nails in one hand, a hooked hammer in the other. Once their nails are in, they might also scratch at your brain with their long nails, digging in to the lobes and folds of your head.

[This would probably give a small penalty to intelligence checks for things that require concentrating, like rituals, reading, translating, etc.]

Schizo Imps - Schizo Imps love nothing more than just talking crazy shit into your ears. The darker and more tasteless, the better. Of course, because they are ethereal, and you are not, you only hear parts of it, and only as a thought in your own head, your brain interpreting signals that you cannot really hear or place. You may never even really hear them at all, but you still feel some sort of deep, intuitive discomfort, that things are never actually quite alright, that your sense of reality is beginning to slip...

[I'd occasionally just give the player a small scrap of paper with some sort of dark yet inane shit on it, not a whole sentence, just part of a clause, enough to make the player wonder what's up, what it could mean. It would of course, mean nothing.]

Ice-Finger Imps - These Curse-Imps cling to your back, and drive their nails into your back, both when danger is near, and when it is totally safe. You would feel only a cold shiver run down your back, the type to set your teeth on edge. The Curse-Imp cackles in glee once the response is learned, when you feel the chill, you can never be calm, if you feel it, danger must be close! ...right?

[I'd probably just do this as written, except it would happen as determined by a die roll. When there's actual danger close, happens on a 3+, if there isn't, on a 5+. Just enough that there is an identifiable pattern, but there also isn't, to keep the players always guessing.]

Poltergeist Imps - Much like the ghosts of tales and story, these imps are tricksters and pranksters. Of course, being on the ethereal, they struggle to clutch much of anything in reality, and at most can only lift the lightest objects. But very occasionally they can pick something of yours up and ruin it, or throw it around. They particularly like to do this to things you really like, or while you're trying to be nice an quiet.

[Again, fairly self-explanatory I think. Each long rest, roll a d6. On a 1, a precious but fragile object is broken and ruined. If you're trying to stealth, roll a d6. On a 1, a small but noisy object clatters to the floor, giving you disadvantage on the resulting stealth check.]

Boiler Imps - These Curse-Imps are practitioners of the ancient arts of Flame-Magicks, not very good ones of course (they are only Imps after all), but they can manifest ethereal flames in their hands, which they use to heat you up. It is only slight, but enough that over time, the heat sets in, and sweat begins to seep up and drip down your face. An uncomfortable stickiness sets in, and no amount of cool rags can seem to shake it. And then, just like that, it is gone.

[Possibly a similar effect to the Headsplitter imp to be honest, though maybe this affects your physical skills rather than intellectual ones (for the sake of having distinct rules if not realistic effects).]

Poxule Imps - Sometimes, a Curse-Imp will consider itself an artist, and will cling to your neck with its thighs and paint tiny red spots on your face. These don't quite make it through to the material world, but they do enough to irritate the skin, to bother your pores enough to sprout you up in a mess of acne and teenage angst all over again. It itches occasionally, but not that much. It does make you look a little bit silly though.

[The best part of this is that I think many players would hate the occasional slip-ins about how their spots blemish their character's faces. Some might embrace it of course, but for those that do hate it, they will hate it. Also, I'd probably give them a -1 or so to many charisma checks. Sometimes, we can't help but take the pimply adult a bit less seriously than we should.]

Malady Imps - If Poxule Imps are artists, Malady Imps are cooks, and they whip up all sorts inside your belly. Most your body can fight off, but occasionally it will seep through you and sicken you. Only a tiny bit though, just enough to make you barf during the night or wake up feeling like a donkey shat on your head in the night.

[Each rest, roll a d6. On a roll of 1, you lose a hit dice, or your HP max is 1 or 2 lower. Nothing serious, but a small annoyance that doesn't cripple you in any way. The main point of the Curse-Imps is to annoy, to psychologically attack the player in a small but noticeable way. Let the real effects come from the players rather than the Imps.]

Drosophilic Imps - These Curse-Imps like to be carried around in your pack. They're never heavy enough for you to ever notice or be inconvenienced by them, but they play with your food, and their fingers are yucky indeed. When you settle down for a meal, you might notice that one of those rations that really should have lasted a couple more days at least, has gone soft and runny. Nothing to do but ditch it.

[Each time they eat a ration, roll a d4. On a 1, they must cross off an additional ration. Nothing too complex in this one.]

Doubt-Sower Imps - These ones are similar to Schizo Imps. They whisper to you like a vulture on your shoulder, telling you over and over that you aren't good enough, there's no possible way for you to succeed, that you'll never be good enough. You never really hear enough of it to make any sense of it, but still, the troubling weight in your belly makes you feel like something is wrong, and you have no idea why...

[These are subtly different, in that these Imps are out to convince you that you're not good enough, rather than convince you that you're mad. When a character with a Doubt-Sower Imp rolls a check they are proficient in, they lose their proficiency bonus if you roll a 1 on a d6.]

Limbclamper Imps - These Curse-Imps like to work by hanging off of your limbs, clutching as tightly to you as they can. Sometimes this will bleed into your material limbs, and a deep cold cramp sets in to your muscels and bones, siezing up your joints and tensing your muscles so that, just for a moment, you can't move. The Imps are experts at timing this for the worst outcomes for you.

[Once per rest or so, when a character tries to use some sort of physical skill, they must do it at disadvantage. Try to keep it from those times that it could lead to outright death, just for when it would have some sort of consequence.]

Skittersight Imps - You could be anywhere, doing anything, when all of a sudden you'll catch just a glimpse of movement. You go to investigate, you run, certain you saw something, but in the end, nothing will be revealed. You will pause, sure there was something there, like the other times. You will wonder when it will come back, if you can catch it next time. The Curse-Imp clinging to your face will cackle that you might never realise it is right there, always with you.

[Save this for those times where the players least expect it, or when they most expect it. Really convince them something is there, and they need to get it. Never let them.]

Beast-Botherer - This one barks like a goat's dying scream, loudly, but ethereally. It barks all day long, and never stops. Now, this is never enough to actually bother a person, animals have much sharper senses than mortals, and they will pick up the wretched grating screams on the edge of their hearing while you are around. They hear the noise coming from you, and the longer you remain, the more and more the beast hate you. The Imp would laugh if its throat hadn't been torn ragged from the constant screaming.

[Something simple like, disadvantage on all charisma checks against animals for you and everyone within 10 feet of you.]

Glass-Eye Imps - Glass-Eye Imps are right bastards. Evil, horrible little fuckers. They clamp onto your head for most of the day, but over time, at night, while you sleep, they sit on your face and scratch and claw at your eyes. They don't do any real damage in any individual night, but they are determined and nothing if not single-minded. They scratch and scratch and scratch, night after night after night, until your eyes are glassy and misted, until you can't see anything at all.

[On a long rest, take a con save that determines how long until the next save. When you would take the seventh save, you go blind, permanently. Maybe have something about a mounting penalty to sight based rolls based on how many saves you've had to take.] 

Bleakspeak Imps - Another type of Curse-Imp that sits on your shoulder and talks to you, only, these ones are grim and dour; they lack the sadistic glee of the others. They speak less, but are heard all the more clearly for it. And when they speak, it is dark, dark words they say, the most cruel and awful things are suggested to their hosts, the things we all occasionally think and are disgusted by. The constant assault doesn't always turn the host into a terrible vessel of these black thoughts, but maybe just sometimes...

[Run them like Schizo Imps, only offer them a small XP bonus for going through with it. Never enough to actually make them do it, but enough that its worth thinking "maybe I should", if only for a moment. Its the considering of the act thats important here, they never have to do it, and given the nature of the Imp, its probably for the best if they don't.]

Rope-Biter Imps - Rope-Biter Imps have very specific tastes; rope. Rope of all kinds and makes and materials. It doesn't matter whose rope either, as long as its close enough to the Curse-Imps host. They cling to you and gnaw on ropes that get close enough to their mouths, full of sharp and crooked teeth. They are rather adept climbers themselves, so pretty much any rope you could touch, they can get into their disgusting maws.

[Very simple, when this character uses a rope, it breaks halfway through use on the d6 roll of a 1.]

Sceptic Imps - These Curse-Imps have improbably (and uncomfortably) long and prehensile tongues, which drip and slop with foul ichors and slimes. So proud are they of their tongues they really, really want to share them with you, all the time, as deep as they can. So be careful when you fight, any hurt of yours is destined for an ethereal bath in Curse-Imp drool. Its as gross as it sounds.

[At the end of each combat or encounter in which the character took damage, have them roll a con save. Their HP max is reduced by 1 for each failed save, which comes back at the rate of 1 + con modifier (minimum of 0) at the end of each long rest.]

Chill-Wind Imps - Have you ever been deep underground, where no touch of the sun has ever dared venture, where the rocks are cold and pallid with the lack of stellar caress? Have you then been relying on your trusty tourch, that beacon of light and hope that you might actually be able to emerge from this dank and dark hell alive, only for it to suddenly, and inopportunely, go out? Its possible you have Chill-Wind Imps. Their whole thing is blowing out candles and flames, you see.

[At the most inopportune moment, roll a d6. On the roll of a 1, all non-magical flames go out.]

True-Colours Imps - These Curse-Imps hide inside your flesh, and have the most intuitive control over their ethereal presence, and they turn it to making it really hard for you to lie. Some of them are loud and bombastic Imps, and have your skin change colour depending on your mood, others are more subtle, and use your smell to give away your thoughts. Some simply grip your tongue in their cruel, grubby little hands such that you physically cannot lie. All of them, take great delight in when the lies are discovered, and the truth apppears, to the detriment of all involved.

[All characters and NPCs and such have advantage on discerning this character's true intentions/feelings.]

Malapropist Imps - Much like True-Colours Imps, Malapropist Imps hide inside your head, and enjoy playing with your tongue. They try to hold off for as long as possible, waiting for the chance to really, really mess up your speech. Sometimes they just can't help themselves, and scrabble at your tongue and kick at your brain, so that the words come out wrong, warped, and misshapen.

[When this character undertakes a speech based activity, roll a d6. On a 1, they have disadvantage on any rolls they need to make, or the effects of the ability are somehow diminished.]

Fumble Imps - These are the laziest of the Curse-Imps. They merely sit glumly on your head, casting tiny little curses on you, bad luck charms, tiny inconveniences. Most get lost in the infinite and infinitesimal gaps between the material and the ethereal, but a few will make it through to make your day just that little bit worse. 

[This character now fumbles an attack roll on the roll of a 1 or a 2, and similarly any other d20 roll is fumbled range in a 1 bigger than normal (since not everyone uses skill check fumbles, thought it would be safer to do it this way).]