Mega Absol

Mega Absol has the highest offensive DPS among Dark-type Mega Pokemon in the game, making it a great choice for any player. Unfortunately its poor DEF and STA stats cause it to not last in battle for very long, requiring good dodging to maintain its Mega boost to teammates for as long as possible. Mega Houndoom isn't far behind in DPS however, and can be another good choice if a bit more survivability is needed for raids. 

Best PvE Offensive Moveset

• Snarl is superior to Psycho Cut due to having STAB and more relevant coverage.
• Dark Pulse is superior to both Megahorn and Thunder for similar reasons.
• Payback is a step down. 
• Return can't benefit from a Super Effective multiplier.