Honesty, it isn't very good right now but I think you can turn things around. There's too many problems for me to point them out one by one so I'll just show what I think your BSS team's full potential is. Also I just need to let this out: Choice Specs Calm Mind Sylveon??? Add some random EVs and you could be the new (nicer) Verlisify.
Gyarados @ Gyaradosite
Ability: Intimidate
Jolly Nature
252 Spe/252 SpA/4 SpD
- Dragon Dance
- Waterfall
- Crunch
- Earthquake
Sylveon @ Choice Scarf
Ability: Pixilate
Timid Nature
252 Spe/252 SpA/4 SpD
- Hyper Voice
- Psyshock
- Shadow Ball
- Hidden Power (Fire)
Pheromosa @ Life Orb
Ability: Beast Boost
Naughty Nature
252 Atk/252 Spe/4 SpA
- Ice Beam
- U-Turn
- Low Kick
- Rapid Spin
Smeargle @ Power Herb
Ability: Moody
Timid/Jolly Nature
252 Spe/252 HP/4 SpD
- Geomancy
- Spore
- Cotton Guard
- Baton Pass
Primarina @ Assault Vest
Ability: Liquid Voice
Modest Nature
252 HP/252 SpA/4 SpD
- Moonblast
- Hyper Voice
- Psychic
- Encore
and your Mimikyu is fine. Welcome back to pokemon database, and hope you like my suggestions. ^^