Can we make a category where we collect all possible items, weapons (for the polar star and knife, you trade them for the spur and nemisis), and heart capsules. I feel like this would lead to many interesting routes.

A category doesn't need to be on the leaderboards for people do runs of it. If this interests you, you could always try it out yourself!

Doesn't mean we shouldn't introduce it as a category...

the reason there isnt a 100% category is because you can't get 100%. you need to trade knife for nemesis, polar star for machine gun, polar star + fireball for snake, etc. you can't have everything at once.

you could do something like "all heart capsules" but I don't feel like that would be different enough to be an enjoyable run.