I think this can sorta include Void Thrashing too. Even though it’s typically one of the fastest missions (not counting speedrunning shenanigans on others).
Here’s how:
- Do the mission as you normally would but don’t kill the last Void Thrasher; or leave more or all alive depending on your skill level (and patience).
- Keep aggro’ing the Thrasher with your armies so that it stops attacking the fortress and only attacks your forces.
- Make sure to only “move” your forces around it and never A-move or hold position or stop. So that you aren’t killing the thrasher.
- Unlike DoN, you’ll need to be active the whole 9 hours. Your ally and you can take turns aggro’ing it. Setup a ton of static def at the enemy wave spawn points, possibly with a secondary army to deal with those.
The thrasher keeps trying to attack your forces, your forces don’t shoot back and take minimal or no damage. And so on.
Would be a crazy challenge to do it with all 10 thrashers but probably do-able with keeping the last 4 alive. And definitely do-able with just the last one.