Here is a little preview of a custom soul I will use in a battle I am going to make (Just to show the souls you can make)
First, find the g_soul sprite and then duplicate the following images... soul_red,soul_broken_red and soul_part_red
And then replace the "red" with the name of your soul and then modify the sprites
And then go into the code and duplicate the script (which script is below) and then replace red with the name of your soul (again) and then remove the "movement with speed" block (but don't remove it if you want it as a base for movement)
And then put the code you want to run during the soul in the if statement
Finally drag to sprite onto g_cursor
And then in a attack set g.soul_col to the name of your soul and then it is done! And fix bugs if there are any.