so you can kill your teammates when they can’t do anything about it? sounds cool
going insane irl to gather some ideas.
Anyway, here are some idea i has
- Dealing damage or taking damage occasionally causes your average ghostly scream audio to play
- Pressing the character menu occasionally makes your character avatar on that menu appear with unsupposed looks (Ex: Lying down with blood, burning or shaking vigorously)
- Npcs in the town might look at you and say the strange dialogue in the chat.
- Eating, drinking a potion or doing anything at all might make unique insanity dialogue appear (Ex: eating food will make a text saying something like “Rotten. Maybe you are no different.”, drinking potion; “Reminds you of those heinous tastes, doesn’t it?”, and jumping down water; “A miracle yet a mockery that you still alive after that day. Not remembering even your saviour.”)
- You crew snitching you (sob)
- food items in your backpack get replaced by atlantean body parts, eating it shakes your screen or causes other insanity effects to happen, cooking meal during this effect may always result in mistakes
- Fishing bobber grabbed by a lot of ghostly hands in place of fish, but when you spam click you catch up the regular fish/item instead. Fail to catch might result in a lot of other hands erupting from water grabbing nothing then going back down cuz funny
- ghost appears in place of a deckhand, maybe with dialogues
oh also, your backpack got shuffled randomly out of order, not scary but mildly annoying
Ideas list:
-In 3rd PV, sometimes if you look at your face, it will appear distended and monstrous for a split second before reverting to normal without warning.
-Gigantic silhouettes of vast figures in the distance, in various poses (refer to Payday 2 Nephilim, Shacklethorn heist figure, Skypeia collossi, Florian Triangle entity.)
-Random attack callouts in chat with nonsensical or scrambled character names, only visible to people under insanity effects. Attack may or may not actually be visible?
-Apparitions capable of annoying but not outright dangerous interactions, such as mobbing a player and dragging them down to the ground if they catch you in enough numbers, Or pulling you into the sky (illusory, and would not actually move you from your position, teleporting you back to the start point of the effect if ended prematurely by insanity wearing off/player fighting back)
-All crew stare towards you, even turning their heads to impossible angles with black, hollow eyes and a creepy expression
-Skybox changes to a black night (with stars conspicuously placed in pairs, like thousands of sets of white glowing eyes staring down at you)
my one:
your sleep paralysis demon spawns somewhere in your current server and slowly approaches you, going through walls and walking on water, visible only to you, if it touches you, you die of an heart attack, can only happen at 4+ insanity
bro is a genuine super villain 
Have a really rare chance for you to hear a sort of quiet but creepy voice saying “hello” or something. If you are wearing headphones it should sound like it is coming from somewhere behind you.
My pfp checks out doesn’t it?
The original antagonist indeed
Hong Kong 97