What is with this Ferrothorn set? That's not a good set at all. Ferrothorn is not gonna need sash as it will be switching in to attacks anyway and you're not gonna stay in against a fire or fighting type anyway. Use Ferrothorn the way it was meant to be, as a wall
Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 252 HP / 252 Def / 8 SpD
Relaxed Nature
- Spikes
- Leech Seed
- Power Whip
- Knock Off / Thunder Wave / Gyro Ball
Don't use Aegislash in ou. There is no reason to use any ghost type in ou that isn't Spectrier or Dragapult considering how good those two are. I suggest using Spectrier considering how brain dead it is to use
Spectrier @ Choice Scarf
Ability: Grim Neigh
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Hex
- Haze
- Will-O-Wisp
- Shadow Ball
Remove Hydreigon. There is almost zero reason to use offensive Hydreigon when every offensive dark type has to compete with dark Urshifu. I'd suggest replacing it with Moltres to protect Ferrothorn from Cinderace along with providing a fairy resist and hazard removal
Moltres @ Heavy-Duty Boots
Ability: Flame Body
EVs: 248 HP / 236 Def / 24 SpD
Bold Nature
- Defog
- Roost
- U-turn / Flamethrower
- Flamethrower / Scorching Sands
Landorus is good enough. Just go with jolly nature as timid is the worst +speed nature you could use on it. Also, use knock off over stone miss on Landorus as it provides more utility
Replace Chansey with Blissey. It's bulk doesn't matter when there is an absolute ton of knock off flying around and there will be times when that knock off becomes unavoidable. If Chansey's eviolite gets knocked off, you are gonna be contemplating life choices. Also, don't use facade or zen headbutt, those will just tickle your enemy
Blissey @ Heavy-Duty Boots
Ability: Natural Cure
EVs: 252 HP / 252 Def / 8 SpD
Relaxed Nature
- Teleport
- Soft-boiled
- Seismic Toss
- Shadow Ball
Don't use offensive Swampert. It is far too slow to be anything of an offensive threat. Every offensive ground type in the tier has to compete with Garchomp and considering your team, there is no reason to use Swampert over Garchomp
Garchomp @ Life Orb
Ability: Rough Skin
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Scale Shot
- Earthquake
- Swords Dance
- Stone Edge / Fire Blast
Use naive nature if running fire blast
Here's a sample team
https://pokepast.es/095d826ec783fae6
The moveset on the paste is what I would use but I suggested options in the answer so just pick what you find useful