Almost all of the categories currently on the leaderboard are for Calamity mod. You can read more specifically if you click on any category, then on 'Read Rules'.
We may accept requests for new categories with other mods if someone has done a run of it, but that's not really implemented very well atm.
If you go to game rules you can see whitelisted mods, which you are allowed to use.
Whitelisted mods: Calamity Mod Music, Recipe Browser, Boss Checklist, Yet Another Boss Health Bar, What Mod Is This From
It may be allowed to use purely cosmetic mods and such, but recommended to stick to the whitelist.
In its current state, the leaderboards only accommodate runs with the Calamity mod. But this doesn't have to be the case. Calamity fits nicely into the level leaderboard layout, but has also warranted a subcategory that applies exclusively to that mod.
Categories for other mods can instead be made