Mega Mismagius
Type = Ghost/Normal
Ability = Purge (doesn't care about opponent's Ghost type when attacking)
Stats = HP : 60
Atk : 50 (-10)
Def : 70 (+10)
Sp.Atk : 165 (+60)
Sp.Def : 115 (+10)
Speed : 135 (+30)
Total : 590
Able To Learn = Focus Blast
This should be the nomal way for Mega Mismagius : Gets in when it's time -> Set up a Nasty Plot -> Sweep. Or it can be a nice revenge killer as well with 130 Speed and 165 Sp.Atk
Weaknesses : Scarf pokemon (TTar, Chomp, Lando-T, ......etc), priorities (Bisharp, Talonflame, Scizor), Special Wall such as Chansey (which can also ruin its day by using T-Wave), Setup sweepers (Anything that can boost its own Speed like DD/Speed Boost/Agility/....), Status (Para cuts its Speed, Toxic puts a timer on it, and Sleep gives your opponent a free switch if they go after you)or Pursuit trap (must not be OHKO by Shadow Ball/Hyper Voice/Focus Blast)
I'm thinking either OU or Uber. TTar should be a problem for Mega Mismagius in any tier, either scarfed or AV. Bisharp is also a check, with Sucker Punch. Klefki with its +1 T-Wave should keep Mega Mismagius away.
Inspiration ? Mismagius is the first pokemon that i've ever fully EV trained myself in Rejuv.