Truant + aron (shell bell) + Dusclops trick room + Mega Beedrill.
Durant using choice scarff + Spd -Spe ; 252 Spd, Spe
Aron lvl 1 shellbell (or berry juice)
"winners don't need training" said by a great Pokemon master out there
(use berry juice for triples) since you are only attacked once per turn with protect and truant and trickroom, no problem. be aware of the mold breaker.
Dusclops Eviolete +Def - Spd ; 252 Def SpA
Pain split (or Spite to finish enemy's PP or Foresight to hit ghost Pokemon)
Beedril (just to be covered) + atk - SpA ; 252 Atk Spd
turn 1 : entretainment + protect
Turn 2: switch + endeavor
Turn 3: trick room + protect
shadow sneak or ice beam + endeavor or swagger or toxic
ice beam or shadow sneak + protect
ice beam + endeavor
Make sure to let the enemy truant Pokemon alive until the very end. Do not get greedy.
Any killer mega should do a good job on beedrill's place if you wish (Umbreon wish?).
problems: Ghost Pokemon, Mold breaker, pressure (ability) to finish your endeavor PP),
try pp max on endeavor