The atmosphere is on point! I really like the visual style you have throughout the dungeon. The movement and possession mechanic seem pretty fluid as well. The only criticism I have would be to somehow inform the player of what to do/where to go in the level itself instead of the separate tutorial option in the main menu. I would also look into spreading out the NPC spawns. On my playthrough it seemed like they spawned together in groups.
Cool concept! I'd love to see more