Chaos class in an interesting one to consider since I put it in to purposefully disturb how combat works. The Chaos class also exists for a special villainous legendary pony I have in mind for later...
The chaos class exists in that weird realm between Ghost, Dark, and Magic but also includes sound based attacks. Master it, and your opponent's strategies will likely be pushed out the window. Check out all the crazy Chaos Attacks planned for BGP on the dev blog!