Your Pokemon choices are actually very viable OU Pokrmon, but the movesets are, to put it nicely, kind of bad.
If you want to keep all Pokemon that are currently there, I suggest making the following changes:
Toxapex
Merciless Toxapex is just so, so, bad. Toxapex should be used as a wall, with very high defenses but pretty pathetic attack stats. I recommend a physically Defensive set that can be used with Blissey to wall much of the metagame. For example, run:
Toxapex @ Black Sludge / Rocky Helmet
Ability: Regenerator
EVs: 252 HP / 252 Def / 4 SpD
Bold / Impish Nature
- Scald / Knock Off
- Haze
- Recover
- Knock Off / Toxic Spikes
Tapu Koko
Defog Koko is not very good for this team since you already have Corviknight and Excadrill on for potential Defog / Rapid Spin. Its synergy is also not very clear. Koko also has weird synergy for this team because Electric Terrain harms Toxapex and Corviknight. If you decide to keep it, run Choice Specs or Heavy Duty Boots:
Tapu Koko @ Choice Specs
Ability: Electric Surge
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Thunderbolt
- Dazzling Gleam
- Volt Switch
- Grass Knot
Tapu Koko @ Heavy-Duty Boots
Ability: Electric Surge
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Thunderbolt
- Dazzling Gleam
- Volt Switch / U-turn
- Roost
Blissey
This set seems fine, but get rid of Leftovers for Heavy-Duty Boots.
Excadrill
This looks like a suicide lead kind of thing, so replace Shell Bell with Focus Sash. Or, if you want a more bulky variant, try something like this:
Excadrill @ Leftovers
Ability: Mold Breaker
EVs: 4 Atk / 252 SpD / 252 Spe
Jolly Nature
- Earthquake
- Iron Head / Toxic
- Toxic / Rapid Spin
- Stealth Rock
Hydreigon
Hydreigon is a pretty good choice for this team, since a lot of it is weak to the Slow gang. However, this set is pretty bad. You can run a variety of sets.
Hydreigon @ Choice Scarf / Choice Specs
Ability: Levitate
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Dark Pulse
- Draco Meteor
- U-turn / Flamethrower / Fire Blast / Earth Power
- Flamethrower / Fire Blast / Earth Power
Hydreigon @ Leftovers
Ability: Levitate
EVs: 164 HP / 92 SpA / 252 Spe
Timid Nature
- Defog / Fire Blast / Flamethrower / Earth Power
- Earth Power / Fire Blast / Flamethrower
- Dark Pulse
- Roost
Corviknight
Currently the set looks like an offensive sweeping set, which is fine. However, if you're not using running Defog Hydreigon or Koko, try using Defog Corviknight:
Corviknight @ Leftovers / Rocky Helmet
Ability: Pressure
EVs: 252 HP / 252 Def / 4 SpD
Relaxed Nature
- Defog
- Roost
- Brave Bird / Body Press
- U-Turn / Brave Bird / Body Press
or if you really want a Bulk Up set:
Corviknight @ Leftovers / Weakness Policy
Ability: Pressure / Mirror Armor
EVs: 252 HP / 4 Def / 252 SpD or 252 HP / 4 Spd / 252 Spe
Careful Nature
- Bulk Up
- Roost
- Brave Bird / Power Trip
- Substitute / Agility
If you have any comments please say so below. Hope I helped!
