Recently geerky42 looked at older logs of the #ln1-routing channel and found a clip of someone doing a very funny slide in a run of The Lady's Quarters IL:

Of course noone at the time even responded when it was posted, because reproducing looked to be impossible. Though if you got it almost as fast as the standard zip, which was being used in IL's up to now, you could save a couple of additional seconds. Luckily I was able to realise what had happened and how to recreate it:

First, the slidebug. Some runners will have come across this annoying glitch that causes you to instantly crouch and get completely stuck. It happens when you start moving in a direction you're facing and crouch at a specific timing. This depends on whether you're sprinting or not, but the walking version is slightly faster.

Note: you should know what a zip is and how to do it before you even consider learning this. Check the prison guide by Nikko for an example.

After doing a slidebug, there is a short period where you can only input movement and nothing else, after which you will still be crouching in a somewhat glitched state for a brief moment. By then doing a zip you can reapply the slidebug effect onto the slide, which will cause the slide to lose friction. Although you will yet again only be able to do movement inputs, your speed will tend to 412 u/s which is roughly the average speed of sprintjumping at full stamina (mostly 432 with a bit of 320 between jumps). This is called a superslide.

Input breakdown: slidebug inputs - release all - wait - zip inputs - wait basically no time - right - crouch release (doesn't have to be timed, doesn't affect the slide)

This is especially strong in The Lady's Quarters because you can just slide through the hole at the end of the hallway chase and keep the speed all the way to the stairs. Any sudden height changes will however kill the superslide, just like walls or you releasing movement inputs. Despite sprint not doing anything during the slide, you can hold it a couple seconds before the slide ends which appears to not slow you down as much.

Using this trick I was able to get the first ever sub-3:50 on The Lady's Quarters IL after 96 attempts, which is about 3 seconds faster than the zip version Nikko did in his run, and 6 seconds faster than the glitchless way used by Poklet.