neat game! i liked a lot of the ideas: alluding to the light switch in the brother's diary and the reveal of what it does stuck with me the most. as for feedback, I think the game could do with some extra noise cues for the final boss, i think that'd improve the atmosphere, and also make the death feel less flat.
also, i found that on the final boss its a lot easier if you stay at the bottom of the room, since the tentacle's down hitbox is a lot more forgiving then the up hitbox. dunno if that is a strategy you intended to be in the game. overall i enjoyed it.