I think this belongs in the RMT, but meh.
Change his item to either Leftovers or Sitrus Berry. Mystic Water isn't really doing anything and these two let Slowbro stay in the game longer.
Replace Toxic with Fire Blast. HAving two Toxic 'Mons is generally a waste of a moveslot, and Fire Blast helps round out your coverage.
Close Combat? Yes. Aura Sphere? Sure. Bulk Up? No. Calm Mind? No. MLuke is meant to be an all-out attacker, and if you want to run a mixed set I would suggest Close Combat / Bullet Punch / Hidden Power [Ice] / Earthquake, and focus his stats more on the physical side.