It’s not too difficult but it’s difficult. Start with an idea. Have a firm idea of what you want your class to do. It helps to make it unique. Once you’ve got your idea down you’ll need to get your character art sorted. For now it’s easy to borrow art from another class then reksin it as you go along. That’s more complicated.
Take a look in the heroes folder. Each hero has their own folder. Your hero will need a folder of their own as well but look at the other heroes’ folders so that you can see how they’re laid out and what goes in them. The .art file tells the game which art to use for each skill. The .info tells the game most of the information about the hero, their stats, skills, pretty much everything apart from camping skills & upgrade costs (which are covered elsewhere). It’s actually fairly easy to understand on teh whole once you’re looking at the info file. In the subfolders the anim folder contains the spine files that make the sprites work in game. In the anim folder you will need to tweak the names of the atlas & skel files to replace their existing class name with your new class name (remembering_that_names_have_underscores_separating_words_instead_of_spaces). You’ll then need to open up the atlas files with notepad and change the class name in the first line of text to match. Change nothing else. The fx folder is for blood splatters and other visual effects that appear when the hero does stuff. The fx files will need to have their class name match and you probably need to open the atlas files and change the class name, same as in the anim folder. The ABCD folders are the hero palette swaps. Once again class names will need to match.
You’ll also want to create a file for them in the upgrades folder (governing the use of the guild hall and the blacksmith), raid/camping (for their camping skills) and localisation (for baking the language into the game). The localisation file, the camping file and the upgrades file are all xml files. It helps to have a program capable of editing xml files and some basic xml know how.
That’s the basics of it. Sorry I can’t go further in depth but it’s almost 3pm and I’ve been up all night and absolutely must get some sleep. Hopefully it’s enough to get you started ‘though.
I’d also recommend getting hold of a class mod from the nexus. Don’t install it. Just open it up and look at the folder & file structure. That way you’ll get to see what the localisation, camping & upgrade files need to look like.