I noticed the speedrun rules ban "level state manipulation", but I have no idea what this is, as there aren't any resources to explain it. What is it? Is it the glitch that spawns you in the wrong place if you die after picking up the level goal, or is it something else?

LSM (Level State Manipulation) allows you to transfer the state from one level to another, but really the "state" is just checkpoints and music. So I am the person who named it but now I think the name is kinda dumb. You can also use LM (live menu) to do it in every level and that also skips the level transition. More detail can be found here: https://docs.google.com/document/d/1XKI6uG274S0r1IdRh7b4zWCHb6zlkPHt0aJr0rTsgY4/edit?usp=sharing but also join the discord if you have more questions because they'll likely get answered faster https://discord.gg/5NFA6K5x7t