Rules: Place Hero teams at ends against each other, red base versus blue base. There are a number of consoles inside the map (6 ish.. same as stronghold). Each console controlled will slow the countdown of your team's nuclear reactor. Holding all reactors almost (not totally) stops the meltdown threshold. First team to go over the meltdown threshold loses.
Objective: Prevent your teams Nuclear Meltdown. (Reactor is like a big bag of HP that can't be killed by character, buffs given by console are like +stacks of resistance but the reactor still takes damage)
Also thought about the possibility for you to need to sit and continue to interact with the console "repair animation with wrench" for it to function but that just favored unbreakable and Bubbles too much. Maybe the control isn't permanent but instead each time you activate the console for your team the meltdown is slowed for 30 seconds before it wears off.
The idea is to keep the battleground moving and reward those who can keep under the radar. Don't quite know how to reward healers in this scenario? Maybe they can directly heal the reactor (well not add moer HPS than it's taking just slow the reactor's DPS) or a NPC at the reactor to slow the countdown. This could work if the reactor you need to save is near the enemy's spawn camp.. i dunno fleshing it out is too hard.
The countdown will ensure that NO match goes over 20 minutes but it also ensures there's no ROFL stomp of either team no matter how uneven the teams.
Choose to be a hunter or a gatherer on your team.
Crowd Control Enthusiast