Feel free to duplicate existing things as a starting place for your own mods (we certainly do!)
From there, you can see all the events, abilities, aspects, campaigns, items, and monsters used in the core game. The Content and Comics Editor is probably the first thing you'll want to look at. For example, if you wanted to modify the assets/data/balance/campaignBalance.json file, you would create a file at mods/user//assets/data/balance/campaignBalance.json. Mods are stored in mods/user/, with a parallel file structure to the core game. Most of Wildermyth's data is stored as json files.
When creating a mod of any kind, the first thing you'll usually want to do is go into the editor from the Wildermyth main menu (Tools > Editor), and create a new mod from either the Content and Comics Editor (Mods > Create New Mod) or the Steam Workshop page (Create New Mod button).
