So apparently fail conditions are if everyone is dead at once, or the doors are breached.
This was a thing. Really fun.
If you play Ana, Biotic Grenades are the absolute best way to get ult charge - fire it into a crowd of Zomnics, bang zoom get ult. Definitely have one stocked up by the final battle if you see McCree also with an ult, because Nano Deadeye is enough to wreck every single Zomnic on the field, plus the Witch, probably the Reaper, and probably Dr. Junkenstein himself. Run over quick to suppress Junkenstein's Monster, though, or he'll heal, and wreck anyone stupid enough to be too close to the door.
S:76 needs to be plopping down Biotic Fields whenever he's nearby wounded allies, even if he's not hurt himself. He and Ana are the only sources of healing, so lessening the load on the Alchemist is always a good thing, especially if she fires a Biotic Grenade at the team.
Hanzo needs to be firing Scatter Arrows so that they hit behind the crates at the center, in the hallway on the right, or in front of Shock-Tires. Zombadiers are relatively common behind them, and they'll wreck face if you leave them alone. If you want to Dragonstrike Junkenstein's Monster, back the hell off and wait for the Gunslinger or the Alchemist to stun him before shooting his face. If you're too close, you aren't going to even touch him.
Try to stay mobile, a bit away from the door, and group up only if you have a Biotic Field running. The Reaper and Junkenstein's Monster both heavily punish grouping, and Zombadiers can easily snipe you if you stand still too long. Also, if you're injured and relying on the Alchemist to heal, stand the f still so that she can shoot you and/or grenade you.