What single thing would you add to game given the chance?

Double blood points every other week.

I'd add in the option to choose your main menu theme from a drop down list of all existing menu themes.

Then the Legion folks can have Legion's theme again and those clown theme addicts can finally recover from withdrawal.

Also it helps the BHVR sound designers rest easy, knowing that their work is immortalized, and not just on YouTube.

Mod support - Custom maps, user submitted cosmetics for workshop, etc.

I would add alternate game modes. Every other weekend, there would be an alternate game mode made available. Once the game mode has been released, it should be permanently available in custom games. There are virtually an infinite number of options available (and I'd love to hear everyone's ideas) but here are a few I've come up with:

Specific Killer VS Specific Survivor using only their perks at rank 3. For example, The Shape vs Laurie, The Clown vs Kate, or The Pig vs Detective Tapp.

Super Speed: Both killer and survivor have 30% increased runspeed.

Darkest Night:The map is pitch black. Survivors all have flashlights that are permanently in the "on" position. The killer has night vision up to 15 feet.

2 killers vs 6 suvivors

Random 12: Both killer and survivors all have 12 random rank 3 perks.

Back to Basics: No perks, items, or add ons.

Casual Mode: All perks are reduced to rank 1. Items and add ons are restricted to common or uncommon. Offerings are restricted to ones that can increase bloodpoint gain.

Entity's Eyes: Strange wards appear throughout the map. Anyone (killer or survivor) that passes within 10 meters of a ward will have their aura revealed to everyone on the map. The wards periodically change location.

Treasure Hunt: No generators on the map. Lots of locked chests are around the map which the killer can see as auras. Survivors must pick the lock requiring skill checks before opening. Most of the chests give survivors a bloodpoint bonus for opening. One chest per map will have a 25,000 bloodpoint bonus. Exit gates are powered after 10 minute timer and chests can't be unlocked after that timer.

Shopping Spree: Survivors are restricted from bringing items into the match and there are no chests to loot. However, there are 2 zombie vendors that spawn in the match. As survivors and killers perform actions that earn bloodpoints, they also earn another form of currency. They can go to the zombie vendors to purchase items and add ons of their choice. Killers can purchase temporary bonus buffs such as 60 seconds 5% movement increase, 40 seconds survivors have exposed status, etc.

Totally Random: All Perks, Items, Add Ons, and Offerings are randomly chosen. Perks are chosen from all possible perks and are at rank 3 (regardless whether the player has unlocked the perk or what rank the player's perks are currently at). Items, Add Ons, and Offerings are chosen from all possible options minus event specific offerings. These Items, Add Ons, and Offerings do not consume the player's resources. They are provided by the entity.

Infection:8 players join a lobby. When the match starts, one is randomly selected to be a random killer with no perks or add ons. The remaining 7 are survivors with no perks or items. There are no hooks on the map, but the killer can Mori survivors in the dying state. Once a survivor is killed they will respawn as a random killer with no perks or add ons. Killers that successfully Mori a survivor earn 1,000 BP. The longer a survivor lives, the larger the bloodpoint bonus at the end.

First Survivor Killed earns 2500 BP

Second Survivor Killed earns 3000 BP

Third Survivor Killed earns 5000 BP

Fourth Survivor Killed earns 7000 BP

Fifth Survivor Killed earns 10,000 BP

Sixth Survivor Killed earns 15,000 BP

Last Survivor Killed earns 20,000 BP

Randomly Selected Killer earns 10,000 BP

Survivors can work on generators, but it takes completion of all 7 generators to power the exit gate. Any survivors that actually escape via the exit gate earn the standard 5,000 BP. Survivors aren't realistically going to escape, nor is it really the goal. The real goal is to be the last survivor alive.

3 Life Survivors: Survivors have 3 "lives". When the killer catches and puts them on a hook the survivor loses 1 life and is put in a ghost world for 45 seconds after losing the first life and 30 seconds after losing the second life. While the survivor is in the ghost world they can not interact with any objects other than ones that can be vaulted. The world appears black and white and the survivor can not see or touch the other players. They can, however, move at 85% normal move speed to explore the map to find the locations of generators, chests, and totems (though ghost players can not tell the difference between active and inactive totems). The survivor will also earn some bloodpoints for distance traveled in the ghost world.

After the timer is up the survivor will appear on a random hook at least 32 meters away from the killers current location. The survivor on the hook will see the shroud indication from Insidious around them. This indicates that the killer can not see them on the hook. In fact, the hook that the survivor is on will appear broken to the killer. Other survivors can see the aura of the hooked survivor and unhook them normally at which point they are back in the game. While a survivor is hooked there is no progress meter and there is no struggle phase. Survivors can attempt to free themselves from the hook, but the baseline success chance is 0% for the first attempt and increases by 1% for each attempt after. Attempts for the survivor to free themselves will take 4 seconds. If all the survivors are either dead, in ghost world time out, or hooked then the killer wins. Survivors hooked in the basement are sent to the ghost world for an additional 30 seconds. Perk Slippery Meat is locked in this game mode (since it wouldn't really do anything).