WorseThanYou worked very hard to make a TAS tool for this game, with a lot of problems the game had dealt him. You basically patch the La-Mulana exe file. The 1.5.5.2 version is most recent, but the 1.3.3.1 version exe file, distributed by GoG, is what you'll need.
This thing reads off a text file, script.txt, which gives a series of inputs. This TAS patch has no save states (there's an inexact state that saves screen location, integer positions, items, puzzle triggers, RNG, and frame count, but other things are impossible atm. We can do frame skips, view all the sprite object hitboxes and the entire grid of 10x10pxs and their state as ground, air, water, etc. Some more features may be added. XY position in floats and their hex value, frame count and RNG is viewable, but if you want more like speed, i-frames, HP and also want to manipulate them for glitch testing, I have a cheat engine table for a load of stuff.
So far, Smurfton has been TASing any% which uses a load of "hermesless raindrops" which nobody except I was willing to do cuz it involved manipulating the fpi in your x-position to reach 0 just as you reach a wall. Meanwhile, I've been working on Time Attack minigames, something nobody really cares about tbh. It's a boss rush where I manage to skip 6 out of 11 bosses. This is possible in RTA, too but would have to use slower, less precise strats and a lot of them are just faster to kill than skip.
So, what I think is the most important section, what is gained from TASing this game over RTA? After all, the game is broken open by raindrops, where you walk into a wall at the exact pixel position to let the wall push you down the floor to wherever you wanna go, and can even do screen mashing, which can pull some object from one screen to another to a limited degree.
First, there are hermesless raindrops, which involes floating point imprecision (fpi) manipulation. Your position is represented in floating points. Numbers like 2.4 become 2.40006103515625. Hermes makes you walk faster so this is used only in the first 3 minutes. More here:
https://www.reddit.com/r/speedrun/comments/5fq20i/bragging_wednesday_november_30/daman2o/
There's also spin whipping or TAS whipping, which is attacking while changing direction in midair. Enemies or objects without i-frames will take the hit every 2 frames, killing or breaking things super fast.
I also have to deal with ideal jump heights, when to start jumping, what type of jump to use, and what speed I should be moving at for how long. Smurfton has been dealing with RNG manipulation using jumps, turning on the ground, and walking on platform edges to create crumb particles and kick up dust.
I've been writing this at a cafeteria while bored so I kept it short. We're in the La-Mulana discord if you have questions.
https://discord.gg/erGns4E
What a wall of text. I should cut this down a bit tbh...
Smurfton's any% TAS WIP:
https://youtu.be/8_QTq7jWtkk
My Time Attack Low-Expert TAS WIP:
https://youtu.be/e7uczf0KKs0 (low level subbosses & super limited equipment)
To get a tldr version of fpi manipulation, just look at the rightmost digits of the x position before any raindrop in the any% vid, or during the 5th boss (floating, glowing boss with lots of hands) in the time attack video. Slowmo might help. Basically, we're manipulating several millionth of a pixel worth of position to match an integer. I like to joke that this is the most pixel perfect glitch ever. What would be more pixel perfect is if the positions were double-precise floats.
Anyway, I only know what I've researched, but the other guys are way better at this than I am, so this is all gonna turn out pretty cool. Haha. I'm just doing minigames, they're doing the main game TAS.
Here's the discord link I just got now!
https://discord.gg/erGns4E
There's a public link to the TAS tool pinned in the #TAS thread!
It's a drawing of Mario overflow jumping into a PU below him!