One hit melee with abilities
Free for all where you primarily kill opponents in one hit with melee attacks. Each character can use some of their abilities to gain an advantage and the cooldowns are adjusted to make it somewhat "balanced". Some characters can use their ultimates as well, but generally the ones that would allow the player to easily kill from range are disabled.
Some characters can fire very slow moving projectiles that will rarely hit anyone, but can sometimes get a kill if you're lucky. Some characters can also use their abilities to tank a couple extra hits. Most of the more powerful abilities have long cooldowns so that they can't be abused too much.
The mode was primarily made without any workshop code though I did have to add one rule to prevent Winston from firing his secondary as currently you can't disable it with the regular custom game settings.
Despite the balancing changes I've made, some characters are ultimately better than others due to their core design, but mystery heroes helps prevent the best heroes from being abused too much and in a match with many players, it's hard to stay alive with a single hero for too long.
I could potentially make some further changes using workshop code for better balance or give some characters more abilities, but I think for the most part it works fine as a casual fun mode in its current state and some random players I've played with seem to have enjoyed it enough to stick around for more than one match at least.
2 characters I could potentially change with workshop are McCree and Symmetra, because currently they can do very little as McCree's grenades and symm's turrets would probably be too overpowered and had to be disabled.
edit: I might make a version of this where some of the cheesier abilities have more limited use. Abilities like Zarya's shield are often just an auto-win unless the player wastes it before getting too close. I could potentially implement a kill-streak system where some of the abilities are only unlocked after gaining a few kills.