Hey there. Exploring the UI of a website you aren't familiar with can definitely be weird sometimes! When looking at the leadboard for a game and a catagory, this site will have a button above the list of runtimes that will show you the rules.

For Enter the Gungeon, one of the rules is:

• "Must play on the default version of the game without Mod The Gungeon installed."

For any runs you want to submit, stay away from mods!