While also being useful in other mu-s?
Fairy-types: Both Xerneas and Magearna force out Mega Sableye by threatening to OHKO it with their STAB moves and do not mind status moves due to their access to cleric moves. Arceus-Fairy and Mega Diancie force Mega Sableye out and can set Stealth Rock, but the former is hindered by Toxic
Mold Breaker and Skill Swap Users: Excadrill can set Stealth Rock and use Toxic on Mega Sableye due to Mold Breaker. Mega Gyarados can use Taunt on Mega Sableye to prevent status moves and set up on it thanks to Mold Breaker as well. Deoxys-S can use Skill Swap to remove Magic Bounce from Mega Sableye and set entry hazards
Primal Groudon: Many wallbreakers can exploit Mega Sableye's mediocre bulk to force it out, but Primal Groudon is an especially notable threat due to it being the most common Stealth Rock user in the tier. It typically carries Toxic to spread status itself, which Mega Sableye's team will generally attempt to avoid
Lucario: Variants of Mega Sableye lacking Will-O-Wisp are taken advantage of by Lucario due to Foul Play granting Lucario a Justified boost and Toxic being unable to put it on a timer
Wallbreakers: Arceus-Ground, Rayquaza, and offensive variants of Priomal Kyogre and Necrozma-DM can overwhelm Mega Sableye with brute force or boosted attacks to KO it or force it out
Pokemon Resilient to Status: The likes of Zygarde-C and defensive Primal Kyogre can outlast Mega Sableye due to them carrying Rest to remove status ailments. With the correct predictions, Substitute users can set up on Mega Sableye, and Facade Mega Salamence can take advantage of status ailments. Arceus-Dark and Arceus-Flying do not mind Mega Sableye at all if they are using Refresh
Source: https://www.smogon.com/dex/sm/pokemon/sableye/uber/
