The fastest RTA route for 100% speedruns grabs ice beam early to pull off this clip, saving a lot of door transitions and having to go into the next room to get a speed boost going.

The following video by ZX497 explains how to pull off the clip. As mentioned in the description, remember that you MUST kill the red orb enemy and grab its drop, otherwise it will not work.

If you want a slightly faster setup, Dragonfangs has one at the 48 second mark here: