Sableye is weak to Fairy-type moves.

Type and weakness

Sableye is a dual Dark/Ghost-type Pokémon. In modern games and in Pokémon GO, this unique typing gives it a single, clear weakness: Fairy-type attacks deal super effective damage to it.

Why Fairy beats Sableye

Before Fairy type was introduced in Generation VI, Dark/Ghost Sableye technically had no standard type weaknesses. Once Fairy was added, that type became super effective against Dark and not resisted by Ghost, so Fairy moves like Play Rough or Dazzling Gleam now hit Sableye very hard.

Any other weaknesses?

Under normal rules, Sableye has no other direct type weaknesses besides Fairy. In some edge cases with older mechanics, moves like Foresight could remove Ghost’s Fighting immunity so Fighting moves could hit neutrally, but in standard play today you mainly just need to remember: use Fairy-types or Fairy moves.