Durant gets Entrainment, so it can pass Truant to the opponent's pokemon. Battle Maison AI will normally NOT switch out, giving easy setups by running protect / setup move, which leads to easy sweeps. Hence, easy BP. 

Turn 1: Durant used Entertainment

Turn 2: Switch in to set-up user (in this case Dragonite)

Turn 3: Protect

Turn 4: Opponent unable to Move, Dragon Dance.

Repeat turn 3 and 4 6 times

Sweep with Dragon Claw/Fire Punch.

Something like this.

[r]

Hi! I'm currently looking for a Truant Durant if anyone has a spare since I want to farm up some ez BP. Thanks guys! 

LF: Truant Durant