[RATE MY TEAM] VGC team opinions?

[Oktay]

I'm a beginner at building teams but I watch team building videos and battles, what I have a hard time kappa with is choosing the moves (knowing what's needed and what's not) and what pokes are a threat to my poke or team because of the stats. Here is my team please tell me what you would change and why (But don't touch my M.Slowbro)

Thundurus @ Sitrus Berry
Ability: Prankster
EVs: 244 HP / 108 Def / 64 SpA / 72 SpD / 20 Spe
Calm Nature
- Thunder Wave
- Thunderbolt
- Hidden Power [Ice]
- Taunt

Slowbro-Mega (F) @ Slowbronite
Ability: Shell Armor
EVs: 252 HP / 252 SpA / 4 SpD
Modest Nature
- Slack Off
- Amnesia
- Scald
- Psychic

PearlyEyes (Sylveon) (F) @ Leftovers
Ability: Pixilate
EVs: 248 HP / 252 SpA / 8 SpD
Modest Nature
- Hyper Voice
- Shadow Ball
- Psyshock
- Hidden Power [Ground]

Arcanine (F) @ Choice Band
Ability: Flash Fire
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Close Combat
- Extreme Speed
- Flare Blitz
- Wild Charge

Tyranitar (F) @ Choice Scarf
Ability: Sand Stream
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Rock Slide
- Dark Pulse
- Fire Blast
- Ice Beam

Ferrothorn (F) @ Lum Berry
Ability: Iron Barbs
EVs: 252 HP / 204 Atk / 52 SpD
Brave Nature
IVs: 0 Spe
- Power Whip
- Gyro Ball
- Leech Seed
- Protect