Biggest threats to the team are probably TG 3 Attacks Manaphy and Spikestacking (especially Klefki)
Other treats are SD Toxicroak, DD Regular Gyarados and CM Unaware Clefable but they are all pretty uncommon.

*Hippowdon > Mixed is possible but it makes the team weaker to Excadrill, Talonflame, Bisharp, Toxicroak
*Rain Dance on Manaphy is pretty interesting (some games were decided by Hurricane missing against Volc / Serp / Gallade, stops Excadrill's Sand and Scizor also profits) but HP Fire is needed so Scizor doesn't sweep and without Energy Ball CM Slowbro is a big threat (tho manageable)
*If Spikes become very annoying you can try out Defog Zapdos. It works vs. Klefki, Gyarados, Talonflame, Bisharp so Hippowdon can go mixed defensive to handle Thundurus better but there isn't really any place for Zapdos because every member is needed.

Nerd (Tornadus-Therian) (M) @ Assault Vest
Ability: Regenerator
EVs: 132 HP / 160 SpA / 216 Spe
Timid Nature
- Hurricane
- Knock Off
- U-turn
- Focus Blast

Rock Paper (Scizor) @ Choice Band
Ability: Technician
EVs: 156 HP / 252 Atk / 100 Spe
Adamant Nature
- Pursuit
- U-turn
- Superpower
- Bullet Punch

Comeback (Reuniclus) @ Leftovers
Ability: Magic Guard
EVs: 252 HP / 200 Def / 56 SpD
Bold Nature
IVs: 0 Atk
- Calm Mind
- Psyshock
- Focus Blast
- Recover

Don Hippeone (Hippowdon) @ Leftovers
Ability: Sand Stream
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Stealth Rock
- Slack Off
- Earthquake
- Stone Edge

What's a Stall? (Manaphy) @ Leftovers
Ability: Hydration
EVs: 88 HP / 252 SpA / 168 Spe
Timid Nature
- Tail Glow
- Hidden Power [Fire]
- Scald
- Energy Ball

Cloudburst (Altaria) @ Altarianite
Ability: Natural Cure
EVs: 64 HP / 252 SpA / 192 Spe
Modest Nature
IVs: 0 Atk
- Roost
- Hyper Voice
- Fire Blast
- Agility