There's hardly a better RP hook than having your character possessed by a demon, genie, banshee or any other kind of unsavoury spirit. The possibility of RPing the character struggling with a shadow in his mind, trying to retain his personality and banish the possessor is a meaty piece of character development that's desired by many.
Sadly, because of its high value as RP device possession is also free game for those who do not really have the idea how to pull it through believably, instead making it a source of drama and extremely often using the device to make the character cursed with awesone by turning the possession into a presence of a superpowered evil side.
I'm writing this guide to help those who wish to portray their characters' possession as a true quandary, an ordeal for their ingame avatars from which they emerge victorious... or not. If all you want as a berserking guide for dummies, you won't find it here.
Before starting[]
In essence, roleplaying possession is quite similar to playing two characters at once: the usual character and that of the demon. The demon "character" is invisible to everyone and the only manifestation of its presence is how the player character reacts to the demon's actions.
If we're treating the demon as a character then we should also give it a backstory. It doesn't need to be extremely detailed and rich, it only needs to answer the following questions:
Why does the demon want to possess my character?
In other words, what makes the character vulnerable and the target of a possession attempt. The answer to this should point to a condition the character is currently suffering from or a past action of the character. The player can show off his imagination here: the noble paladin can be experiencing a moment of weakened resolve. A Warlock may be seen by the demons as a possible agent. A mage may have struck a deal with a demon lord, a very good deal because the mage has to give his soul away willingly when he feels like it. It could be an entirely random assault, the possibilities are endless.
What is the goal behind the demon's efforts?
Now we are looking at the matter from the demon's point of view. What does it want to accomplish by possessing this very character? The answer is usually very simple here: the demon wants to dominate the character. Dominate? No, it's the wrong word. Dominate implies control over the body while the character's mind struggles against the demon's. No, the demon usually wants to conquer the character's mind and soul. To change them. To make the character willingly step out and pledge allegiance to the demon's master. Definitely not to drive the character into berserk from time to time after which the character feels only slight pangs of conscience for what he had done but express them very loudly...
Acting it out[]
So you have decided to RP possession. Congratulations, but be warned that RPing it out in the proper mood and setting takes a long time, several weeks, months even! Changing one's mentality is a slow task even for a fiend that is a master in possessions. You will also have to have a group of acquintances around you, people who RP with you often and have an easier time noticing that something is wrong with your character, the reason being that people completely strange to your character will more likely dismiss him and shrug it off rather than react.
The progress of the possession itself can be divided into several phases, each of them meaning a greater degree of change and control the demon has over the character, shown by intensifying behaviour and visible signs. I would like to remind you here: as with all guides, the phases described here are just hints, advice and directions, not final and fundamental rules.
An extremely important note about emotes: you should strive to reduce metagaming to a bare minimum. Never, ever inform others what exactly happened to your character. Every action should appear completely irrational and out of context unless ICly explained by the character afterwards
And now, without further ado:
Phase 1[]
So, the character's soul has been spotted by the demon. The character will find out soon enough. Wherever he goes he will be stalked by his dark patron. The feeling of privacy is gone, the character always feels a presence, the chill gaze of the demon on his back. Shadowy silhouettes in the edges of his field of vision. It's the demon, waiting for the opportunity to act.
The character, of course, should react accordingly. Constant watchful peering around and over the shoulder, the occasional shiver. Symptoms of mild paranoia. The demon has no control yet, but soon it will.
Phase 2[]
So, the demon had finally decided to act. The character will slowly begin to lose his will and his personality will change. At first all that the character can notice are silent voices in his head, strange feelings. Let him shiver or feel a prick of anger when looking at a holy man. Let him hear a soft "Kill him!" when he sees his best friend or, more likely, a random person. Will the character listen? Probably not. But he will begin to have doubts and others will see. A momentary steely and evil glare, an untimely shiver or twitch, a hesitation when touching an object of holiness. The character will hardly notice, but others will.
Phase 3[]
Whether the character listens or not, in time the whispering will only become tiresome for the character. Thus, the demon needs to act. And in that phase the best course of action is to let the character feel simple, mindless fear. A nightmare so dreadful that the character soils his pants and shivers for the day after. A fit of paranoia in the waking hours. "They are all after you, plotting behind your back!" Yes, the whispers increase in intensity, not words but phrases. In RP the character's antics become more pronounced, make him look around the tavern with a hint of murder in his eyes. Draw his weapon and stare at best friends with panic in his eyes.
Phase 4[]
But are whispers and mental trauma the only effects of a demon's actions? No way, that would be too beautiful! The character should have doubts. He should slowly but steadily come to the conclusion that Good and Evil, that the society, the common good are only mirages and illusions and the only being that matters is the character himself.
So we have a paranoid character that's being torn by doubt. He can have so much, he only needs to reach out for it! But he still worries about the price. Should he betray what he believed in all his life? Abandon his ideals? No, he should resist. He should and he must.
But whispers are only a very gentle form of the demonic manipulation, the fun has not yet started.
Phase 5[]
Let's divide this phase in two: the first part are situations that happen outside the character's consciousness. Let him one day awaken pointing a sword towards a best friend, a superior, a random person. How did he get there? You RP'd something walking the body of the character and speaking with his lips. That should give everyone a signal that something dreadful happens with the character. Let him awaken a few times like this, with the knowledge he could have dome something terrible. Do this a few times in sight of your character's fellows and watch as they grow suspicious and distant to the possessed character. Well, not possessed yet but very soon.
And what if the character starts experiencing holes in memory? He will lose track of conversations or forget what he planned to do. You can RP this out easily: simply make the character conveniently forget. The character finds himself in a graveyard and doesn't know how or why he found himself there. And why is Roderick reminding me of some promise? I didn't promise anything!
Remember: all what happens above should be sporadic! At least for now. Other characters need to be worried and suspicious, not angry.
There will be time for more drastic steps, but there's much more to be done. What happens outside the character's consciousness is one thing, what happens within is much, much more serious. One day, the character will run out of the smithy screaming in terror: the eyeballs of the shopkeeper had just burst, his cheeks flooding with blood and his lips grimace in a toothless smile. After a moment everything returns to normal, of course. Another day while, say, inspecting the armour of his subordinates, the skin of his reflection in a polished pauldron will ooze away, revealing muscles and blood vessels. And again, everything is alright in the blink of an eye. One word: Hallucinations. The nightmares your character has been experiencing for some thime become his waking reality. In the face of madness people think strange things but the character might maintain enough reason to try to banish the demon.
Here a hint about emoting: never emote exactly what your character sees. Let others find out later, when the shivering and panicked possessed is being tended to.
Phase 6[]
And what if not only the mind but also the body starts to malfunction? While sitting at a table let your character stand up abruptly, flail his arms smashing everything from it and shout a few incoherent words in a mighty voice. Everyone will be shocked, including the character. And that's the point. Other's trust in the character should evaporate like a snowflake in a flamethrower once he starts to behave uncontrollably. It's important not to let the trust return. The actions need to be repeated. Make the character smash his fist into the counter while in an inn. Make him rip the pages of a book he's reading. At a game of dice make him throw the dice at a co-player.
Phase 7[]
So the mentality of the character breaks asunder. Fear is his daily bread. And while the character grows weaker and wearier, the demon that lodged itself in his soul grows in power and is soon able to maifest its abilities. Items in the vicinity of the character begin to move on their own. Strange noises are audible when near him. Whispers, cries, laughter or agonised moans? Or maybe unnatural odours? Or maybe all fire near the character turns fel green? If anyone had any doubts about the character's condition, this will remove them.
Epilogue[]
How will the character deal with this? Will he turn to a holy man for help and healing and if so, will the holy man agree? Or maybe he will turn the character in as an abomination that needs to be killed? Maybe he will ask a powerful wizard for help? Will the wizard agree? And what will he want in return? Or maybe the character himself will try to perform a cleansing ritual? But how? And the reagents are absurdly difficult to come by! Getting rid of a demon can be the lynchpin of an interesting adventure, so get to work, roleplayers and build a lethally dangerous path to freedom!
And what if the character turned to the leader of some dark cult for help instead? Of course he will patiently explain that the Legion or any other dark entity had sent the demon because the character did not live in concordance with the evil tenets of the entity. If the character willfully enters the path of evil, there will be no need for a demon to coax him onto it! And this will allow for RP again, this time on the side of darkness. This might be different and more difficult than what you had RPd before, but also fresh and new.
If you want to RP possession much long and hard work awaits you, but the reward is one of the most intense and touching adventures you and your character ever experienced!