SM OU Rate my sand team please

[Eclipse77]

This is my first weather team but I haven't had much luck with it. What changes should I make?

Hippowdon @ Smooth Rock
Ability: Sand Stream
EVs: 252 HP / 80 Def / 176 SpD
Impish Nature
- Stealth Rock
- Earthquake
- Slack Off
- Toxic

Excadrill @ Steelium Z
Ability: Sand Rush
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Earthquake
- Iron Head
- Rock Slide
- Swords Dance

Garchomp-Mega @ Garchompite
Ability: Sand Veil
EVs: 4 HP / 252 Atk / 252 Spe
Naive Nature
- Earthquake
- Dragon Claw
- Stone Edge
- Fire Blast

Rotom-Wash @ Iapapa Berry
Ability: Levitate
EVs: 248 HP / 204 Def / 56 Spe
Bold Nature
IVs: 0 Atk
- Hydro Pump
- Volt Switch
- Will-O-Wisp
- Thunder Wave

Tapu Koko @ Shuca Berry
Ability: Electric Surge
EVs: 104 HP / 12 Def / 176 SpA / 216 Spe
Timid Nature
IVs: 1 Atk
- Thunderbolt
- Volt Switch
- Hidden Power [Ice]
- Dazzling Gleam

Tangrowth @ Assault Vest
Ability: Regenerator
Shiny: Yes
EVs: 252 HP / 28 Def / 228 SpD
Sassy Nature
- Giga Drain
- Knock Off
- Grass Knot
- Hidden Power [Fire]

 

[IronBullet]

Welcome to Smogon! I'm locking your RMT for the time being as the forum rules require that you provide in-depth descriptions for each Pokemon to explain their roles. Please read the rules carefully and take a look at Team Showcase to see the level of detail we require. PM me with updated descriptions and I'll be happy to unlock this.