Sableye is known for having its infamous Ghost/Dark typing, along with Spiritomb. This Pokémon also has the Prankster ability, making it very useful for crippling opponents with status. So here's a moveset for Sableye in Gen 9 NU.
Sableye (M) @ Focus Sash
Ability: Prankster
Tera Type: Ghost
EVs: 252 HP / 252 Atk / 4 Spe
Adamant Nature
- Shadow Sneak / Sucker Punch (Good priority, STAB but I would personally pick Shadow Sneak)
- Will-O-Wisp / Thunder Wave (Both statuses are great for crippling opponents.)
- Knock Off (Great move overall, since most of all competitive Pokémon bring a useful Item.)
- Fake Out / Foul Play (Fake Out if to break Sashes, and Foul Play for great damage.)
Tera Ghost is because you won't really be using Tera in this set. Fake Out might be better in usage, but Foul Play is much better in terms of damaging. Personally I would pick Thunder Wave for the status move, halving the speed of other speedy Pokémon. Extra EVs in Speed are to outspeed some other Sableye. Although, for a more statusing Sableye..
Sableye (M) @ Focus Sash
Ability: Prankster
Tera Type: Steel
EVs: 248 HP / 252 SpD / 8 Def or Atk
Careful Nature
- Thunder Wave (Cripples speedy opponents.)
- Will-O-Wisp (Great to have with Thunder Wave, cripples physical attackers like Eelektross.)
- Recover (Amazing healing.)
- Shadow Sneak / Knock Off / Fake Out / Confuse Ray / Foul Play (Your choice, but Knock Off, Shadow Sneak and Fake Out are the primary options.
Careful Nature is to maximize your special defenses considering the amount of Special Attackers that are in NU. Steel is the most defensive type, great for staying longer in battles. Although, you wouldn't really use a Tera on Sableye anyways.