Made two terrible mistakes on my first run, which left me so close to victory I could taste it.
First, I accidentally top-decked too much area damage, which resulted in my early strategy of “redirect ethereal bonds from Nightmist to Gloomweaver to shut him down” collapsing at the worst possible moment, right before Gloomweaver picked up Strength of the Grave and then killed two of his own cultists to rapid-play more things at my face.
Then, with everyone but Nightmist dead, I sacrificed Master of Magic to the Drum of Despair to try and keep her HP up, only to realize very soon afterwards that I’d misremembered Lifeline’s incap and I couldn’t destroy equipment for cards, only Ongoings. This left Nightmist without the +5 cards I had been hoping for.
At the very end of the game, Gloomweaver blasted himself down to 4 HP, then hit Nightmist for 5 damage and killed her. She had the Amulet of the Elder Gods out and a single card in her hand, so one more card and she would have killed him instead…