Standard difficulty. I was doing my sub 3 run for the points when i came across an odd glitch, doesn't seem like anyone has mentioned it. At the point when you get the iron key from the piano and then use it for the first time, in the iron insignia door with the scripted lady D. I shot her using the fully upgraded infinite ammo SYG-12 3 times (I believe) and she did her stun animation, and seemed to stand up in the doorway, and then blinked out of existence. she did respawn a few minutes later in a different part of the castle, but it might save a second or two. I'm considering REV as my first speedgame so if i've found something potentially useful that'd be sweet.

EDIT using whatever is most up to date version as of 22/5/21.