You skip the fight with skip mode and hope it gets fixed in any of the future updates (or updates not yet uploaded here).I don't know if anyone else has gone through this part of the story, but when you want to start the mission the characters have 1 percent of life and it is impossible to pass the level, does anyone know what to do?
Alternatively just try turtling - you stay and let the fiends come to you - with Throbert (or whoever got better defence items) taking the front position to make him tank blows. Then you let your Family Jewels heal him (equip vibrator on her so she gets 2 healing skills) and leave the killing to Good Vibes and Florence without the Machine.