So I cleared snow veil catacombs/sanctum, killed the draugr overlord and company, got to the puzzle door and Mercer Frey opened it no problem. My problem is, whenever I try to cross that door to enter the final room where Karlilah presumably is, I instantly die. HP bar doesn't even pop up, just instant death. I've tried everything I can think of, even turning god mode on, to no avail. Tried reloading from an earlier save too. I need to finish this quest to continue with the thief guild line, and now I've got Mercer Frey stuck following me everywhere, which is slightly game-breaking. Any ideas? Is there a console command to spawn npcs?

Thanks.

leaver the dungeon, dismiss your follower. return to the door with mercer.

^This. Just go with it.