A short introduction and guide on the relatively new tech called 'Zerohop' or '0hop' I found that allows you to reach engine cap (600 u/s) without cheats.
What it allows you to do is keep all of your speed by sprintjumping (full jumps not short jumps/tap jumps) repeatedly at less than 10 stamina, and even build up more speed slowly. At most stamina amounts it doesn't matter how soon you can jump, inbetween every jump there is a short gap where the game sets your speed to running before you can jump again. You can even try jumping before you land, if timed right the game will do a frame-perfect jump for you since there is a small input buffer for that. However it will still probably not work.
When I started running this game I started noticing that I could keep my speed at less than 10 stamina. This happened mostly before the crank at rope and with the old jump strat in kitchen. I never bothered to investigate since I thought this game was pretty much solved already as opposed to Little Nightmares II which had a new find every week pretty much. Boy was I wrong, and especially after I found kitchen clips I wanted to see this game destroyed as much as possible. After having zerohop happen on accident once again I finally decided to test it. As it turns out, there is a particular animation/state that allows you to jump before the speedcap of running is applied. It is doing full sprintjumps at less than 10 stamina without a chase flag*. Doing this repeatedly not only allows you to keep your speed indefinitely but even builds up a fixed amount of speed each jump because every jump in this game simply adds a fixed amount of speed and the devs assumed your speed is reset every jump.
To actually gain the most speed in a zerohop you will need to time your jump just before landing so the game does a frame perfect jump for you. Unfortunately there is no easy way to do this except practice the jumps and get a feel for the timing. If you do happen to jump early and lose your speed because you didn't jump, don't panic or start spamming jump. Get back to sprinting speed first, since it's still 80% speed compared to full stamina, then try again.
Each jump in the zerohop chain will give you about 28 u/s of added speed if done right. Speed chart: https://imgur.com/a/4HyiEKT
*Chase flag refers to the type of jumps you do at low stamina while being chased sometimes, with which zerohopping doesn't work.
Because of this there are the following optional routing changes to the standard stamina management route:
Fridge to lever before Rope split: Timesave is about 1 to 2 seconds depending on how fast you climb the box at the lever and how clean your jumps are. This one is very tough and doesn't even save that much because you need to get stamina back in order to jump the gap after the lever without climbing. The fact that the ground you have to jump over is unequal doesn't help in the slightest. So probably the last timesave in the game to go for. This is mostly just to flex on pre-2021 runners that sub-3:00 rope is easy and 2:57 is the real shit. Currently rope wr is 2:54.907
Bread to cages before prison split: Timesave is about 2 to 4 seconds depending on if you keep your speed across the gap or have to abort and take the safer jump. The ground is mostly flat but if you do jump from the doorstep thing, remember that you need to jump later on the next jump or else you will missjump. The area after the doorstep is in turn a bit higher than the bridge itself. The areas before and after the doorstep are the same height.
Medusa 2: About 3 seconds of timesave if you get it as shown in the video, with the edge slide. Doing it this way is pretty difficult because you need to slide off the edge of that step perfectly to get up to the speedcap as soon as I did. Usually you will just have to keep jumping normally off of those steps and the timing for that can be a bit rough.
Prison end: Very minimal timesave but there is not really a downside to dissuade you from doing this one since you would drain your stamina there anyway. You can just keep jumping and not have to worry about stamina at the very end there like you used to, this one is pretty easy because the ground is completely flat.
Hull: This is a spicy timesave of possibly as much as 8 seconds if you hit everything like a TAS, perhaps the most difficult of the bunch though. The cause of this is the fact that the jump timing constantly changes based on your speed and position on the pipe. The reason you save so much time is partially because some parts are perfectly angled to give the maximum amount of acceleration and I will get into that more in the conclusion.
Guest area: I'm just linking the entire IL here because I can. Especially the start and chase are important though. Throughout this chapter there are a metric ton of triggers that reset your stamina to 100 and we have to work around them as well as we can.
The zerohops at the start maybe save a second overall so I feel like you should keep those for later, but they are easier than the fridge zerohops for example. The current bottle community gold doesn't use them but it gets a fast climb at the lamp which saves more time than this because of stamina complications. It's currently disputed whether or not it's actually a second slower to do this because you lose 2 seconds getting a slow climb at the lamp, which is caused by trying to do the lamp swing too early.
The chase however can save you maybe 4 or 5 seconds if you zerohop both halves pretty well. First of all, there is a chase flag set on you when you do fat guy skip, this is why I reset to checkpoint at the elevator, because it clears that state in which you can't zerohop. If you don't intend on doing any zerohopping after fat guy skip, do not reload to checkpoint as in that case it would just lose you time.
For the first half, you can try to drain some stamina in advance while you're going up in the elevator. Then just start jumping. Be wary of the doorsteps, if you jump just before them you might land after jumping right away which can mess you up. At the end of the first half lies a stamina trigger that resets your stamina back to full. This happens just before the raised platform. Speaking of which, if you get the perfect lineup into the room with the raised platform it's possible to zerohop just before the trigger and make it up on the platform without climbing.
The second half is a bit more difficult and saves less than the first, but its goal is to make the second cabinet fall as soon as humanly possible which involves keeping speed down the stairs which is not the most fun activity I can think of, oh well. If you really want to do this but zerohopping down the stairs is too much, try waiting a little longer after the table to start jumping and it should still save time. Just don't forget that the first cabinet that should drop behind you can kill your run whenever it feels like it.
On the last table before the lamp swing getaway is the biggest difference between stamina management and this, since you start with no speed so you just have to get to sprinting speed and start a very slow zerohop chain. There is also a way to zerohop into the lamp but that's precise. After you start swinging on the lamp, jump off as soon as possible to avoid the soft fall. You can keep the speed from the swing by doing two zerohops into the door opening but I don't get it in the run which might've cucked the 4:16 in this case.
Conclusion: Zerohopping can really be done anywhere with the ln1 engine, even in the DLC, but the limiting factors of timesave are: Stamina management, acceleration/speed and chase flags.
Stamina management for certain spots where zerohopping is technically reasonable, like before chair skip, is sometimes just impractical. In that part there are just too many small rooms to gain any real speed, and chair skip without full stamina is very hard.
Acceleration and speed preservation is also a roadblock. With what we know right now zerohopping up stairs isn't humanly possible and maybe impossible altogether because you need to do full jumps. With how generous jumping in this game is though, it's probably possible somehow. Going up a slope like the pipe in Hull is beneficial to acceleration however, because the game adds some speed for every jump (around 32 u/s), in theory this means that the acceleration gets higher as a slope gets steeper, but for humans it's very hard to time zerohops up a slope, especially with big speeds involved. If you have more speed you need to jump exponentially more frequent due to acceleration and the fact that you're moving into the surface you're jumping from faster. If that makes any sense :D
Chase flags/triggers were put into the game by the devs presumably to help casual players not die in a chase. They give you extra fast jumps at low stamina for a certain area where you need to avoid an autoscrolling chase. Unfortunately the jumps you do in that case don't allow you to zerohop so for speedrunners it ironically slows us down. The triggers we don't know how to quickly clear right now are the Roger elevator chase and the second half of Lady's quarters. As soon as the chase AI spawns in you automatically start doing those jumps instead of zerohops.
This trick has by no means been solved yet though. The DLC's have this tech in them as well and even though I have no extremely clear memory of them, I do remember how big the levels are compared to the main game chapters. Since I don't run those chapters yet I haven't actually gone through them to test certain spots. I am also not perfect so there could be some spots in the main game. I'm overlooking right now that end up saving time with zerohop.
Even with limited routing we already have 20-22 seconds (if done perfectly) of timesave.
I wish you good luck with practice!
