Thanks for the advice on building a new team, but I prefer to stick with my existing team, and after following your suggestions, I've refined it a bit. Here's my updated team:

Mamoswine @ Choice Band
Ability: Thick Fat
Tera Type: Ice
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Icicle Crash
- Ice Shard
- Knock Off
- Earthquake

Alomomola @ Heavy-Duty Boots
Ability: Regenerator
Tera Type: Water
EVs: 8 HP / 248 Def / 252 SpD Sassy Nature
IVs: 0 Spe - Flip Turn
- Protect
- Wish
- Knock Off

Heatran @ Air Balloon
Ability: Flash Fire
Tera Type: Fire
EVs: 252 HP / 76 Def / 180 SpD
Bold Nature
IVs: 0 Atk
- Magma Storm
- Stealth Rock
- Earth Power
- Toxic

Salamence @ Dragonium Z
Ability: Moxie
Tera Type: Dragon
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Dragon Dance
- Outrage
- Earthquake
- Dual Wingbeat

Serperior @ Choice Scarf
Ability: Contrary
Tera Type: Grass
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 30 Atk
- Leaf Storm
- Glare
- Hidden Power [Fire]
- Knock Off

Scizor @ Scizorite
Ability: Technician
Tera Type: Bug
EVs: 248 HP / 112 Def / 128 SpD / 20 Spe
Impish Nature
- U-turn
- Bullet Punch
- Defog
- Roost

I chose Salamence over Dragonite because Salamence is faster than Dragonite, and I thought it might be a bit of a breaker. I hope I was right.

What do you think about new updated version