I checked the head screen that appears at the start of the story mode, and it wasn't there. Then tried to find it in the character customisation screen, and stilll no luck. I also tried to complete the featured arena mode to check if it would unlock it, it didn't (obviously, because it didn't say that it would, but I'm trying all the possibilities). I played with some people in a cooperative match and some arena matches, and still didn't. What else can I do?
Sorry if there are any mistakes, by the way.