I want to ask why you who do this category don't add the infinite ammo option? It would save a ton of time in The Power of the Underworld (and some time in The Silent Riddler).
Also, why not get the Rocket Launcher in The Lost Temples of Nubia so you can rocket jump to the exit? With infinite ammo that could help the amount of rocket jumping too, naturally (since you only get 5 rockets for picking the weapon up).

sounds like an extremely arbitrary idea to add something which is normally coop feature. Variables makes sense if they just represent how you can play this game, like SSD/noSSD, console, game version (GOG,Steam, other), patch, OS in some cases (Undertale) and so on. But this is just as arbitrary as, let's say, adding DRM scorpion as a variable. And I also don't see ANY benefits of infinite ammo for full run, since you have enough for arena levels that you mentioned and you don't lose time cause you still need to hit triggers. And for Lost Temples, if you do a propboost you end this level faster anyway.

I don't agree with it being a typically co-op feature...? It's available in both modes.
Anyway, I overestimated the time that can be saved with proper fights. Watching follon's WR run again in the fights I mentioned, the difference wouldn't matter.
About Lost Temples, yes, the rocket launcher is only at the end of the level. And then I don't really know how to rocket jump and if there are surfaces that you can use for that last part.
Maybe a more interesting idea would be to add new categories such as SP on higher difficulty (There's a great speedrun on Mental), Survival maps and coop?
I see a lot of speedruns for those categories on YT that may deserve a spot here.