Darkrai

Like a nightmare about to take over the mind of an unsuspecting dreamer, Darkrai looms over the anti-Ghost and anti-Psychic metagame... but, sadly, the shadow that it casts isn't exceptionally long. It was once one of the better Dark Type attackers, but Brutal Swing basically sealed its fate as an old-fashioned Dark Type attacker; good, but low on the DPS side. Hoestly, Darkrai's only real hope for the future is that its Signature Move, Dark Void, turns out to be great someday. It would also have the honor of giving Darkrai a strong Dark Type Charged Move so that it can stop using Shadow Ball.

Best PvE Offensive Moveset

• Snarl is better than Feint Attack on Darkrai.
• Shadow Ball is among the best moves in the game, perfect for Darkrai's role as a Dark / Ghost attacker.
• Dark Pulse is slightly weaker, even with STAB, but it can perform better in very specific scenarios due to an early damage window.
• Focus Blast has poor type-synergy on Darkrai and should be TM'd.
• Sludge Bomb has no use on Darkrai

Snarl is the preferred fast move due to its significantly higher energy gains. 

Dark Pulse and Shadow Ball provide similar coverage, but the former is superior stat-wise due to STAB and lower energy cost. Focus Blast is recommended for its wide coverage even though it demands huge amounts of energy. Sludge Bomb can be used to hit Fairy-type Pokemon super effectively, although it is not enough to secure a win against either Pokemon.