Ultimate Citizen Dawn versus the variant Void Guard at Insula Primalis!
FIGHT!
This is a rough one. I beat it on my third try by completely changing my usual strategy for dealing with Dawn. Normally I aim to get her to flip and unflip as soon as possible and keep the citizens off the table to avoid their nastier pair interactions, but in this case, that's suicide. Dawn hits back when you kill citizens, and she needs so many citizens in play to unflip that you'll die while she's still invincible.
The way I won was to only remove the most dangerous citizens (Hammer, Tears, and Anvil, mainly), making sure to stay under Dawn's limit so she wouldn't flip, and keep focusing fire on Dawn herself. I think I only used Malpractice Medico's power once in the whole game; I thought was more useful to me to get his Healing Pulse in play and keep the team upright than to blast out lots of damage, but I may not be using RedMed to his full potential.
The Mark 2 Shadow Projector blocked a ton of damage, often self-damage, because I tend to use it on Medico (keeping him from hurting himself while he heals the team) or Mainstay (to avoid Shard Strength's cost).
Now, some of this is going to depend on how Writhe's deck reshuffles after you pull his shadow cloak out. If you can use Grasping Shadow Cloth once or twice, you can really strangle Dawn's forward progress, and if you drop one at the right moment, you may even discard the Aurora that she plays around turn 6. It's just luck if you do that at the right moment, though, without multiple replays to figure out her deck order and have the Cloth in hand when you need it.
Mainstay is pretty great in this fight. I kept his Shard Strength up for nearly the entire match until the Aurora blew it away. I used Mano-a-Mano a couple times to take out weakened citizens or just deal some damage to Dawn, though of course that's a risky play if you don't have an equipment to blow it up when the risk is greater than the reward.
But the real star is of course Idealist. It's a trick to keep enough Concepts in play to keep charging the big robot, but the work is worth it when you can hit for 8, 9, or more damage every turn.
The environment is a problem, and I had to take Lava damage more than once, but everyone but Medico has at least one way to remove environment cards, so keeping that under control isn't a huge problem. Just make sure you leave a weakened citizen around for the raptors to gnaw on.
I managed to win right after Mainstay took himself out dealing one last mano-a-mano hit to Dawn after a Lonesome Highway that really smacked her hard, and weathering the counter-attack until Idealist could bring the giant robo in for significant overkill. Everyone was in single digits after the Aurora wiped out Medico's ability to keep the heals going and we were all short on cards thanks to multiple blinding blasts, but they managed to end it just before Dawn could come in for the kill.