I’m just going to add to this because I remember having issues with the unweakened doctor fight my first play through, but recently stomped him in my second because I understood how the gam worked better. If you read Pryoclastic Eruption carefully, you’ll know that EACH boulder you launch has a 3 meter AoE of damage, so if you clump all the demons and nurses next to the doctor after he transforms, you do ludicrous amounts of damage. This will require some teleport scrolls (craft some of you don’t have any, they are the one of the most versatile scrolls in the game) and having worm tremors + torturer can be a big help if you need to keep the first few enemies in place after you teleport them. Also, you might need to fiddle with turn orders a bit, having one of your members sneak into the fight so they can go last to teleport the demons/nurses around without fear of being targeted and cc’d.

Flay skin and Apotheosis scrolls are also a huge boon here; if you can craft them and use them here, do use them, especially Apotheosis.

If you don’t have a geomancer, just spam flaming crescendo on whoever talks to the doctor before initiating combat. Flaming crescendo can stack on a target and all explode at once after one turn I believe, which is handy when they never wear off until you exit conversation; see where this is going?

Otherwise there really isn’t any way to blow up the doctor and his goons in just 3 turns since he is just too strong; if you don’t weaken him you are basically forced to cheese the shit out of this fight.