It is mandatory to the extent that you have to pick something other than your canon abilities. Canon abilities are nerfed, and Astoria-powers are not working at the moment! How wild you get is entirely up to you. You could go full bright blue tiefling warlock, or you could be a human fighter! It's up to you.

Finally, just to be clear - you do not need a character sheet! Our cap is simply so we don't have anything too overpowered, and the race/class is mostly for narrative purposes. We don't expect people to be D&D experts overnight to play in Acata. :)