To make Custom Abilities, you first need to give it a definition in the abiltext.rb file, and an ID in the PBAbilities.rb file - this will create the ability without any effect. To add an effect to ability, you can add it to one of the scripts file. For example, in a Move altering ability, you could add it to PokeBattler_Battler.rb or PokeBattler_Move.rb if you'd like. The Primal Dialga/Palkia mod has a good example, if you'd like to see that. To add it to a Summary display(where you would normally view the pokemon's ability, stats, etc ingame), you would need to edit PokemonSummary.rb. I may be wrong in some of these, but there are many mods that can provide a more clear example than my description. Hopefully, this helps! Good luck with your testing ^_^