Musharna is in my opinion, one of the best Pokemon in the tier. Her overall bulk is good enough to be a great defensive 'mon. I've experimented with different teams in NU and my best teams have Mushy on them. My favorite set is the 'standard Calm Mind' set above; the EV spread gives her decent physical bulk and her special bulk is already good and if you get in a CM boost or two, she's extremely hard to bring down on the special side.
Overall, she's a great asset on most teams, an absolute must on defensive teams if you ask me.