SOTN/Reverse Shift Line

Reverse Shift Line or RSL for short is an important glitch used in multiple skips for the Alucard categories. It can be used to skip over rooms or go out of bounds. Its primary usage is for the Death Skip and the Relic Skip.

Not to be confused with Shift Line, another glitch that can be used to go out-of-bounds or skip areas.

Mechanics

During screen freezes like a Level Up, Heart Refresh or Shield Rod spell Alucard is able to move for one frame at the current speed without affecting screen scrolling.

The screen starts shifting to follow Alucard 129 pixels away from the edge.

If Alucard enters a screen freeze state while moving away from the end of a screen at the scrolling point then exits the screen without going further away, that causes Alucard's room index to be offset on the next screen effectively causing him to appear on the other side of where he usually would. This can also cause you to be placed inside of a wall, causing you to zip downwards. This glitch is sensitive to subpixel values so a setup is required to assure a successful attempt for both activating the screen freeze and for exiting the room. Depending on the setup and subpixel values this trick can have a 2 frame window instead of one frame.

step by step visualization

Starting location, Alucard's X pos is represented by the orange line and is at 126px away from the left edge. The blue line represents the position after the scrolling activation. We first hold forward.

On the next frame (in this case one or two would work) we press heart refresh.

After moving in the HR animation our X coordinate is at a point when shifting would start occurring normally. We buffer a backdash out of the screen freeze and exit the screen from the left side to activate the glitch and warp to the left side of the next room.