Rate my OU team in Showdown

Question

Heatran @ Air Balloon
Ability: Flash Fire
EVs: 248 HP / 252 SpA / 8 SpD
Modest Nature
- Flamethrower
- Flash Cannon
- Dragon Pulse
- Hidden Power [Ice]

Tyranitar @ Tyranitarite
Ability: Sand Stream
EVs: 248 HP / 252 Atk / 8 Def
Naughty Nature
- Aerial Ace
- Stone Edge
- Hidden Power [Ice]
- Payback

Metagross @ Metagrossite
Ability: Clear Body
EVs: 248 HP / 252 Atk / 8 SpD
Adamant Nature
- Meteor Mash
- Hammer Arm
- Zen Headbutt
- Explosion

Starmie @ Leftovers
Ability: Analytic
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Reflect Type
- Ice Beam
- Hydro Pump
- Psyshock

Venusaur @ Black Sludge
Ability: Chlorophyll
EVs: 72 HP / 4 Def / 252 SpA / 180 Spe
Timid Nature
- Sunny Day
- Solar Beam
- Giga Drain
- Sludge Bomb

Chansey (F) @ Eviolite
Ability: Serene Grace
EVs: 252 Def / 252 Spe
Timid Nature
- Soft-Boiled
- Protect
- Toxic
- Seismic Toss

Comments

Be careful about your Ground-type weakness.
And maybe Ice Punch / Earthquake > Hammer Arm? (on Metagross). You could also replace Explosion with Rock Polish / Agility because you would want your Mega-Evolution to stay alive as long as possible.
I'm not so sure about Hidden Power [Ice] on Tyranitar, you could always use Ice Punch / Ice Beam.
Also, you shouldn't have two mega evolutions (or the other one would become dead weight since only 1 mega evolution can be used)