So I would like to request a game, Starward Rogue. It's Binding of Isaac in space, basically. The vanilla version has 9 starting mechs and 5 difficulty levels, which would make for an unreasonable 45 categories. DLC adds another 3 mechs. How would you go about reducing the amount of categories? Maybe only allow the easiest difficulty, or rather include difficulty as a run note?

Hardest difficulty tends to be a good benchmark for speedrunning. If there are difficulties that aren't "substantially different" then that could be a reason to not include them.

Maybe use subcategories for either the mechs or the difficulties, or both. Since theres probably Any%, 100% etc I would suggest using both in that case

in stardew vally they use subcategory in marriage % https://www.speedrun.com/stardew_valley#Marriage :)