Hey! Thanks for checking out our engine.
All of the things you mentioned are technically possible to add if you have GameMaker Studio 2. The project file (.yyz) is available for download for free on the page.
However, it might not be the best idea to use the engine if you are looking to make a traditional fighting game. You'd have to get rid of a lot of the "smash bros specific" code for it to work, and it might be more difficult than just coding a traditional fighting game from scratch.