So far possible problem mu's I've come across are robin, wowo, red hood and atro. Atro seems worse of the bunch ATM but robin isn't far behind, obviously early and could be doing things wrong but the space radien weakest in they strong so its rough going
Something that is def not a possible problem is fate, that is a definite problem. Worse than atro for sure imo (this coming from playing it as both fate and raiden)
There some other mu's I'm not too sure if even or 4-6 Like deadshot or cpt cold.
(
@IrishMantis is having none of me saying vs cold isn't a winning mu for cold ATM though)