Let's have a look at Calyrex, first off stats, base 100 HP and base 80 everything else, so above average HP and mediocre at everything else. The only thing I see it being good at is a relatively tanky Special attacker, so here you go.
Calyrex @ Leftovers
EVs: 128 HP / 252 SpA / 128 Spe
Timid Nature or Modest Nature
- Giga Drain
- Calm Mind
Psychic - STAB plus deals with the powerful fighting types of the tier, like Blaziken (but be careful with him).
Giga Drain - STAB and self recovery for the above average HP.
Calm Mind - Set up for extra bulk, but be careful who you set up against.
Reflect - Set up for the rest of your team as well as yourself, for Defense that you don't have EVs in.
I know, subpar moveset, no coverage, but it's a subpar Pokemon with no coverage.
Now is my favorite form, Calyrex Shadow Rider, an absolutely monstrous Special Sweeper, so here you go.
Calyrex-Shadow @ Focus Sash
Ability: As One (Spectrier)
EVs: 252 SpA / 252 Spe / 4 HP
- Astral Barrage
- Nasty Plot
- Pollen Puff
Astral Barrage - STAB, base 120 power with 100% accuracy without any drawbacks? obvious first pick
Nasty Plot - Raise Special Attack 2 stages, with Focus Sash it's guaranteed, perfect
Psychic - More stab, with a chance to lower sp.def, if they even survive the hit
Pollen Puff - Weird but it covers Dark types
Basically come in on something preferably that can't hit you and set up Nasty Plot, then proceed to sweep, or don't set up if you don't have to. Dark type? Kill it with Pollen Puff. Ghost type? Astral Barrage. Normal Type? Brute force it with Psychic.
Now for Calyrex Ice Rider, a once again monstrously powerful but this time physical attacker, but it's super slow, so time to prey it has decent priority moves or your running a Trick room team.
Calyrex-Ice @ Leftovers
Ability: As One (Glastrier)
EVs: 252 Atk / 128 Def /128 SpD
- Glacial Lance
- Swords Dance
- Close Combat
- Zen Headbutt
Glacial Lance - Same deal as Astral Barrage but slightly more powerful, physical, and ice type
Swords Dance - Nasty Plot but for physical attack
Close Combat - I know it lowers the defenses but it covers 3 of it's 6 weaknesses
Zen Headbutt - Decent Stab, but that's really it
Yes, it doesn't have much coverage for fire,bug, or ghost, but that's what switching is for, I only recommend this set for a trick room team though or else you'll get outsped and OHKO'd by one of it's 6 WEAKNESSES
I hope these helped you make a decision!