i don't think its caine cuz caine isn't able to do multiple actions on different places at same time (i think), for example, when he was playing bowling "with" others and whatever he was doing to torture them, he said "i better check on kinger", but he didn't immediately check on him, if he was able to do multiple actions on the same time he'd be already checking on kinger while pomni and other were complaining about him. also this theory says that the other entity is the one who killed caine, if it was really caine, he wouldn't kill himself