I've been developing a One Punch Mode on the PTR for about a week now.
Definitely the most popular mode I've made so far. Doesn't work that great with small teams, especially when there's an imbalance, but so does the rest of Overwatch. :V
This current batch of settings allows for all abilities that there is no reason to actively disable like Biotic Field, Supercharger (everything kills in one hit) and so on.
Capture Speed: 75%
Respawn Time: 60%
Disabled: Genji, McCree, Mei, Roadhog, Symmetra, Torbjorn, Zarya and Zenyatta. (All of them have lethal, ranged alt-fires you can't turn off even if you disable everything for them, eg, Icicle, Fan the Hammer, Orb Volley, etc.)
General Hero Settings:
Ability Cooldowns: 10% (unless otherwise modified)
Damage Delt/Received: both 500%
Health: 25% (10% causes Reinhardt to complain about his shield health. Everything still kills everyone in one shot.)
Movement Speed: 225% (Slight increases should be ~230-240% if you use them)
•Ana: Her perk is Nanoboosting.
Rifle/Grenade/Sleep Dart (Does ranged damage, sorry. Gotta axe it.) all disabled.
300% Ultimate Charge.
Potentially increase speed slightly.
•Bastion: The fastest character.
Disable sentry gun, reconfigure and tank mode. 300% movement speed.
•D.va: Perk is baby D.va giving her a one-time second hit, and defense matrix to counter Orisa.
Disable Boost (OP as hell for this mode) Fusion Cannons and Self-Destruct. (I've had some people suggest adding it since everyone can move so fast it's easy enough to avoid, and it would let her re-Mekka, but I've never tested it.)
•Hanzo: Wall climbing perk. Practically flies after wall-climbing.
Disable Scatter Arrow, Sonic Arrow (would be nice if it didn't do damage) Storm Bow and Dragonstrike.
Potentially increase speed slightly.
•Junkrat: Perk is Mayhem. (Explodes when killed, genuinely dangerous when everyone's melee)
Disable Concussion Mine, Frag launcher, Rip Tire, and probably Steel Trap (or give it a longer cooldown. I've only tested it a little bit with it on, people didn't like it much.)
Potentially increase speed a bit unless you enable traps, in which case decrease it.
•Lucio: Group Speedboost and wallriding.
Disable Sonic Amplifier and Soundwave (OP as hell, don't let people try to convince you to enable it. Just turns the match into all-Lucio mode moreso than usual.) and Crossfade if you don't want him to be able to slow down at all :3c
Set his base speed to 200% (Faster than almost everyone with speed on, fastest when amped up) and 75% cooldown on Amp. (Disable Amp on live servers, the aura is way too big.)
•Mercy: Heros never die. Also gliding I guess.
Disable Cadeuceus Staff (because otherwise she can use her blaster).
300% Ultimate charge rate. Gives her a rez for approximately every 10 kills.
•Orisa: Halt! It doesn't do damage! Therefore it's usable here. But bump up the cooldown to 20% otherwise it's a little much.)
Disable Fusion Driver. (That's it. Everything else is irrelevant to this mode, lol.)
•Pharah: You can fly, you can fly, you can fly ♪
Disable Rocket Launcher and Barrage. Concussive Blast with at least 50% cooldown if at all.
Hover Jets maximum time, 25%, recovery time, 20%, Jump Jets, 50% cooldown. (Because otherwise she can just hover-contest until you get another pharah, hanzo or widowmaker to punch her out of the air.)
•Reaper: Temporary immunity
Disable Hellfire Shotguns and Death Blossom
Wraith Form: 38% (3 seconds between wraithing. No one's really tried him so far in my testing, feel free to tweak.)
250% speed (because he's pretty dang underpowered.)
•Reinhardt: Big area swings, but attacks much slower than everyone else and is a very easy to smack target.
Disable Fire Strike and Earthshatter.
Charge cooldown: I've been doing 50% lately, but it can't be too low otherwise it becomes incredibly overpowered.
Decrease speed to 180%.
•Soldier 76: Marathon Man. (AKA, Sprint.)
Disable Heavy Pulse Rifle, Helix Rockets, and Tactical Visor (it overrides the disable primary fire option, apparently)
Potentially increase his speed a bit.
•Sombra: Stealth mode
Disable Machine Pistol.
Disable Hack & EMP (not that these are necessarily against the spirit of the mode, but it gives her too much advantage.) or you can try alternatively disable stealth/translocator (if you want her to be the hero-disabling-hero.)
Stealth cooldown 20% (so you can't stay hiding nonstop) and Translocator cooldown 25% (so it can't be spammed too much to be fun)
•Tracer: Blink spam!
Disable Pulse Pistols and Pulse Bomb.
Blink Cooldown 30% (about half a second per charge. Spammable but not too frustratingly so.) Recall has a fixed minimum cooldown of 4 seconds presumably so you have a starting point to rewind to.
Potentially slow her down a bit if she's feeling too much of a must-pick.
•Widowmaker: Wallhax and Grappling
Disable Venom Mine and Widow's facebattle.
Ultimate Charge 400%
•Winston: Primal Rage (and optionally Jumppack)
Disable Tesla Gun.
If you only have Primal Rage, 350%. Otherwise, 200%, and JumpPack to whatever you feel is appropriate, I've been doing 60%.
Decrease speed to 180%
Updated a bit 3/26 since I discovered the primary fire changes made it to live. Tried to remember what all tweaks I did besides lowering the global speed to give Bastion a perk but its hard to remember 'cuz you still can't save them.