It's nice enough.
Sash ShadowRex is nice enough on some builds like HO, as Focus Sash lets it withstand an attack from threats like Ditto, Sucker Punch Yveltal, Marshadow, etc. However, you'll have to take care of hazards on your field, as they'll make the Sash useless.
I'll suggest one change here, though. You can add Baton Pass in the last moveslot, to give your Nasty Plot boosts to Pokémon such as Xerneas and/or Yveltal, making them extremely threatening. In NatDex AG, Dynamax Life Orb Yveltal is a great wallbreaker, and coupled with the boosts from the Calyrex-Shadow, it becomes an extreme powerhouse.
If you don't have LOrb Yveltal on your team, though, there's no issue. Fitting Yveltal on your team isn't much of an issue, as it's extremely flexible and has an exceptional amount of roles which it can fulfil, like the aforementioned LOrb wallbreaker, or a Defensive Calyrex-Shadow check. If you do have an Yveltal on your team, the problem's sorted and you can run Life Orb on it. Even though it'll make the Yvetal a shaky ShadowRex check, with Sash Calyrex + the Yveltal (if there are no hazards on your side), any opposing ShadowRex'll have problems sweeping.
New set:
Mint And Tucker (Calyrex-Shadow) @ Focus Sash
Ability: As One (Spectrier)
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Astral Barrage
- Nasty Plot
- Psyshock / Draining Kiss
- Baton Pass
To be played along with,
Yveltal @ Life Orb
Ability: Dark Aura
EVs: 4 HP / 252 SpA / 252 Spe
Rash Nature
- Dark Pulse
- Oblivion Wing
- Heat Wave
- Rock Slide / Focus Blast
Hope this helps!
