In an arcade run I eventually got to a room where one enemy was unable to be target or even hit. All my spells and attacks pass through it without dealing any damage, and my summon would not target it. The enemy could still attack and even damage me. As far as I am aware there was nothing special about this room, no bet with Bishop or anything. This was the only enemy in the room that acted this way, and there was another bush monster and a stone statue. I was unable to progress the run due to the door not opening because there is still a "living" enemy. I died to activate a time stone and when I revisited the room I could kill the enemy.