Shadow Sableye

Shadow Sableye is an interesting little Pokemon, but its performance  is poor. As an attacker, it's even below Gastly just to put it into perspective. That said, it looks absolutely amazing.

Best PvE Offensive Moveset

• Shadow Claw is slightly superior to Feint Attack, offering slightly higher DPS, slightly less energy gains, and similar coverage.
• Foul Play is strictly superior to both Shadow Sneak and Power Gem, offering significantly better damage and more relevant coverage respectively.

Best PvE Defensive Moveset

• Feint Attack is better than Shadow Claw, with higher damage and energy gains.
• Foul Play is strictly superior to both Shadow Sneak and Power Gem, offering better damage, lower charge times, and an earlier damage window.
• Power Gem can offer better coverage against Dragonite and offending Fairy-type Pokemon.

Shadow Claw performs better than Feint Attack most of the time. Their damage output is the same, but the former leaps ahead with energy gains compared to latter. While this doesn't seem like much, in practice the difference is very noticeable, resulting in charge moves being used much sooner. 

Foul Play is Sableye's best charge move, which costs only 45 energy and benefits from STAB. Power Gem is now a viable (and good!) option on Sableye thanks to its buff in Pokemon GO: Max Out. Shadow Sneak is terrible.