Gourgeist-Large @ Choice Band  
Ability: Frisk  
EVs: 252 Atk / 4 SpD / 252 Spe  
Adamant or Jolly Nature  
- Power Whip  
- Poltergeist  
- Shadow Sneak  
- Trick / Rock Slide

Gourgeist-Large  
Ability: Frisk  
EVs: 252 HP / 4 Atk / 252 Def  
Impish Nature  
- Will-O-Wisp / Toxic 
- Synthesis  
- Power Whip  
- Foul Play / Poltergeist 

Gourgeist-Large @ Weakness Policy  
Ability: Frisk  
EVs: 252 Atk / 4 SpD / 252 Spe  
Adamant Nature  
- Power Whip  
- Poltergeist  
- Flame Charge  
- Rock Slide / Shadow Sneak

Other options: Choice Scarf