Can you help me improve my OU Balance team?

Question

Alomomola (F) @ Leftovers
Ability: Regenerator
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
IVs: 0 Atk
- Protect
- Toxic
- Wish
- Scald

Chansey @ Eviolite
Ability: Natural Cure
EVs: 252 HP / 252 SpD
Calm Nature
IVs: 0 Atk
- Seismic Toss
- Toxic
- Heal Bell
- Soft-Boiled

Garchomp @ Garchompite
Ability: Rough Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Earthquake
- Dragon Claw
- Fire Fang
- Swords Dance

Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 252 HP / 92 Def / 164 SpD
Sassy Nature
IVs: 0 Spe
- Spikes
- Leech Seed
- Power Whip
- Gyro Ball

Gengar @ Choice Scarf
Ability: Cursed Body
EVs: 4 HP / 252 SpA / 252 Spe
Modest Nature
IVs: 0 Atk
- Shadow Ball
- Sludge Wave
- Focus Blast
- Hidden Power [Ice]

Tapu Koko @ Electrium Z
Ability: Electric Surge
Shiny: Yes
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Thunderbolt
- Roost
- Hidden Power [Fire]
- Dazzling Gleam

I'm not at all convinced of Gengar and Tapu.

Comments

It's a stall attempt, anything else I can change?

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This is not stall. This is just standard balance. I'm not sure you know what stall means.

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Well, I don't know much about this. Then I should direct this to a balanced team as you say, I suppose.

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In stall, you use only defensive Pokemon and maybe one sweeper. You have Blissey, Alomomola, and Ferrothorn as walls, and Garchomp, Gengar, and Tapu Koko as sweepers. So it’s balance.

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Stall means that almost your entire team is dedicated to switching into various attacks and healing off the damage. So they usually leave very few move slots and EVs for damaging the opponent. You obviously have a lot of attacking moves and attack EVs, so this team isn't stall.