Helpful Tools

In addition to the Modding API, there are many useful tools to help you creating mods.
Some of the popular ones include:

Unity Explorer

Essentialy like a unity editor built into the game, this tool allows you to view how the game is built from the editor side. You can find out object names, component values and all kinds of things that will help you. You can get its BepInEx version here.

Assembly Publiczier

This tool takes Assembly-CSharp and creates a publicized version of it, which means that all of its private fields, methods and more will become public. Cuphead hides many of the important fields and this tool allows you to use them without reflection. You can get it by following the instructions here.

Unity Modding Template

This is a unity project that contains audio clips, scripts, map and level templates, an asset bundle generator and more. You can use it as a project to make your asset bundles in and it's especially helpful when creating custom maps and levels, since you have everything you need already there. You can download this unity project here.