>>21050554A variant would be:
Sableye @Sablite
Bold 252 HP 252 Def 4 SpA
-Calm Mind
-Recover
-Shadow Ball
-Dazzling Gleam
Considering it loses Speed and that it's SpDef isn't going up too much (+15 for 80 base with a locked 50 HP is my guess), it really can't afford to Nasty Plot unless you somehow manage to force two free turns, one to Nasty Plot and one to Recover, while you still have Prankster; you WILL be 2HKO by every special attacker, all of which outspeed you. Calm Mind loves the bulky set and Recover, and Dazzling Gleam gives you perfectly neutral coverage on all non-Pyroar mons. You trade the versatility of early/mid game burns for perfect sweeper coverage.
For a Nasty Plot set, I'd be tempted to run instead:
Sableye @ Sablite
Calm 252 HP 252 SpDef 4 Def
-Rest
-Sleep Talk
-Nasty Plot
-Shadow Ball/Dark Pulse
Honestly, I don't think Nasty Plot will be very viable on it unless it, but this is how I'd play it. Nasty Plot with Prankster on something you don't fear or something that fears you may be a Will-o-wisp/Taunt variant. When it's no longer safe to Nasty Plot, Rest or Attack if you think you can survive the attack. Now you Mega-evo to get either a priority Sleep Talk or a priority Rest while also proc-ing Magic Bounce. Sleep Talk your way to KOs, and hopefully you'll KO threats so you can live to slow Rest again later.
Restalk Calm Mind benefits more from Recover due to less dead turns to synergize with how otherwise slowly Calm Mind boosts before it becomes a threat. The benefits of Rest (status immunity) is largely moot when you have Magic Bounce. May still be a viable set though.
Perhaps the meta will shift to allow Nasty Plot M-Sableye to shine, but I'm banking on Calm Mind being better and more reliable. Most of the normal counters to Calm Minders (Taunt, Encore) are dealt with by Magic Bounce, and Unaware mons hate getting burned, though Clefable still gives you trouble.
