i think there should be a killer, that can insta down you, but only if you do something specific, these are my main ideas:
1. a killer that has a passive power that sometimes gives you tasks (for example, do 20% of a gen in x amount of time), and if you dont complete a task youll get marked for a y amount of time, this killer also could have an active ability thats maybe a projectile that hurts you if you are marked, but doesnt insta down (unlike m1 attacks), or maybe give you a task in chase (for example, dont drop a pallett for 3 seconds), i know this could be really disgusting with certain builds, but if the tasks are stuff the survivors actually need to do, then i think it would even encourage players to do important things.
2. a killer that can insta down a survivor when they a have a sin (i took this from the grimoire), if a survivor does something that angers this killer (maybe even other survivors, but i dont know what that should be), they would get aswell something like the ritual circles, and you can repent your sins theer, this would be a normal slow down, something that pig has for example, this concept is not that fleshed out, but i hope you see what i mean
3. and finally, this killer would be the hardest to implement, but it would be probably the coolest, each survivor gets a uniqe icon in the hud, and the killer would have 4 different powers, similar to vecna, you could cycle between these powers and each one would insta down the survivor with the same icon as your power, and if you use an other power you would only damage them (maybe if its too op, then you couldnt even down them, just with the power that you need), also these powers would be probably like an axe, maybe a simple lunge, vecna's skeletons, nemesis' whip, maybe even like a hillbilly-ish chainsaw sprint, and the catch is, you cant use m1 attacks, so this killer would require you to learn a lot, but rewards you for trying other playstiles
let me know your thoughts!

3:18 bro was just chilling 😭

3:18 wild Claudette spotted

Technically wesker can also insta down, since if a healed survivor is affected with the black things and it turns red grabbing them picks them up instantly

You only looked at Exposed for instant downs, but actually Trapper is also a pseudo instant down killer since a healthy survivor who gets caught in a trap can be instantly picked up and hooked provided the Trapper is in the area when it happens. So even though Trapper doesn't "Expose" survivors he can in essence "bring a healthy survivor to a hook state" with a single trap and pickup.

And then there's dredge with its exposed add on and 4 exposed perks. It's pretty gross but really fun. Since a good few of them give you map information too like Dragon's Grip. You can pop over in an instant. Couple that with Devour Hope + Make Your Choice since you can hook and instantly be far, far away. And then you can be back in an instant to down the rescuer. Friends 'Till the End is another good choice for a bit more exposed but both it and the hex could be replaced with something like surge if you wanted. Or, if you keep friends till the end, the hex could be swapped with another obsession based perk like furtive chase since getting occasional undetectable outside of nightfall is terrifying.

I can't promise you'll win a lot with a build like this. Dredge is still dredge after all. But to dredge mains winning can be secondary. They play dredge to be generally spooky and then focus hard on the TTV during nightfall to scare the hell out of them and put on a good show for their viewers. Bring horror back to the game and all that. And a teleporting killer that can bonk you once and down you? Terrifying.

Bonus points if your other add on is Field Recorder to start the game off in nightfall.

I think something like Hopeless Exile (from the latest Grimoire) but everyone in the dimension is instadownable (basically meaning the killer must leave the field of play to 1v1 a survivor, losing all their map pressure and snowball potential in exchange for the exposed)

A gen siphon killer. He kicks generators and as it regresses it fills a meter, upon filling the meter you can activate it at anytime applying a reverse batteries included (5% speed buff around non completed generators). Make it so the generator only needs to regress for 30-60ish seconds, and have the timer be about a minute. Anyone within this range can be insta downed.

5:31  I don’t remember the exact build, but in the earlier versions you could glitch perks and addons, and if I remember correctly you could put a nurse addon on billy and make his chainsaw silent

I love running Friends till the end and Furtive Chase on The Dredge. It is sooooo good

The only insta down I like in dbd is dramaturgy. Having it as a risk possibility in that perk to me is very fun.

3:16

what

The only way to fix ghostface is by making him go slightly faster while using stealth power and make his speed add-on obsession based, and instead of being revealed, it requires 2 people to kick ghostface off of power. (Also mute the breathing)

Billy but silent? Looks over at Apex muffler

A Killer that moves slow but passively creates spots on the ground within its terror radius that if stepped on grant exposed for a set period of time so you have to watch the ground as you loop. addons can make it so the survivor is exposed as long as theyre standing in it, or increase the duration of the exposed after they leave it, maybe addons that make spots linger outside the terror radius for a set amount of time or increase the speed of the spots spawning and disappearing.

0:41 Dredge, Wesker and Springtrap if you count their special grabs (which in my opinion is better than an insta-down because it automatically starts the carrying animation).

I know Hillbilly and Oni dont "expose you" but my point still stands. bhvr arent making anymore one shot killers, and we can see why🤷🏽

salutations jittleyang!

Wesker has an Instadown. Full Uroborous  infection Ames for a one shot.

My suggestion for a killer ability would be that it might be an upgrade killer that has to complete ingame quest type of things to power up for example the first power up is like break 2 pallets or something when the killer reach a certain threshold its power becomes strong enough and unkocks the instadown ability
My second suggestion is interactive choice system where ingame you can change your power to an instadown power but it becomes slower atack and its cooldown increses or something but ypu also have to earn the ability to change the power