To add an ability, just follow the existing format, where you write the ability's defName between tags.
Typically, an ability's def name will be written as TM_TheAbilityNameInCamelCaseWithoutSpaces, but some abilities do not follow that format. If you want to give a class an ability, you have to find the ability's defName in the class' abilities file. The most important thing is the abilities. Congratulations: you just added a class to the custom class roster! Unfortunately, it is but a copy of the Shadow right now. In the Shadow's file, copy everything from the first to the last, and paste that underneath that last. The file is heavily commented with explanations from the mod creator. The Shadow is implemented as a custom class, so you may take inspiration from its file, called TM_CustomClassDef, found in the CustomDefs folder.
