Even though most people see the most potential for Mega Sableye in CM sets, it could also work as a dedicated anti-SR Pokemon, as it can wall many SR setters, such as Landorus-T, Garchomp, Ferrothorn, Gliscor, Chansey, Celebi, Terrakion, and Hippowdon. With a specially bulky spread, Mega Sableye even walls SR Clefable (barely) and SR Heatran, and even though it can't do much to Clefable, it can cripple Heatran with Knock Off and slowly KO it. And even with a SpD spread, it still has good enough bulk to prevent SR from defensive Lando-T, and any passive SR setters (Chansey, Celebi, Hippowdon, Gliscor, Ferrothorn). Knock Off / Recover / WoW are musts on such a set, while the are many options for the last slot. Taunt can be used, to shut down stallbreakers such as Gliscor, Mew, and Talonflame, all of which Mega Sableye walls easily, and let another Pokemon come in and deal with them, as well as shut down any defensive Pokemon that Mega Sableye walls but can't beat one on one, so that another teammate can safely come in and take care of it. Foul Play can be used to prevent SD Talonflame, Mega Charizard X, Refresh / Sub DD Mega Salamence, Sub Mega Gyarados, Sub Mega Heracross, and SubSD Hawlucha from setting up on you. Sucker Punch is a decent option for very passive stall teams that have no other way of dealing with speedy sweepers and has great synergy with Magic Bounce. Metal Burst can net surprise kills, as Mega Sableye is surprisingly hard to OHKO. Toxic can let Mega Sableye beat more quickly the defensive Pokemon it walls instead of going in a PP stall war, such as Chansey, Hippowdon, etc, forcing them out eventually, as well as crippling special attackers and Fire-types.
Aside from preventing SR from going up, Mega Sableye walls most stallbreakers, such as Mew, Heatran, Gliscor, and Talonflame, as well as some very threatening sweepers / wallbreakers, such as Mega Gallade (only counter to this beast actually), Mega Medicham, Breloom, Bisharp, SD Mega Scizor, and Iron Tail-less Lucario.
And with Mega Sableye's great overall bulk, it's not hard at all to lead with it, so that you can MEvolve asap and make sure you can actually keep SR off the field when the SR user comes into the field.
For all those reasons, Mega Sableye seems as a fantastic Pokemon for stall. Keeping SR off the field without any passive play (Rapid Spin and Defog users give free turns) is wonderful, as it gives way more freedom for switching around and makes using great defensive Pokemon that are SR weak much easier, such as stallbreaker Talonflame, TauntWoW Victini, AV Tornadus-T, and defensive Gyarados. With the physically defensive spread, all you need to do is pack a Defog / Rapid Spin user to beat Clefable and maybe Heatran (if you lack a cleric, PhD M-Sableye still walls Heatran), and you have every single SR user covered for good. Also, covering extremely threatening stallbreakers, sweepers, and wallbreakers is great, as well as access to STAB Knock Off, Taunt, and WoW.