Anon... All my team members were lvl 28-30 when I did fought Mimipyu.
Try using that Psych Up TM you
should have obtained earlier to get that boost in everything. You could also open up with a bunch of stat-lowering damage moves to simultaneously break its disguise and lower its stats at the same time. Even if one of your bros gets thrown into the trash, the stat reductions will stay put on Mimic(you). Or you could use a Magneton use Metal Sound on it and destroy it in like one to two hits.
The possibilities are endless, OP. If you STILL can't beat it, then see >>31368267. 