Landorus-Therian (M) @ Choice Specs  
Ability: Intimidate  
EVs: 252 HP / 252 SpA / 4 SpD  
Modest Nature  
IVs: 0 Atk  
- Hidden Power [Ice]  
- Grass Knot  
- Earth Power  
- Psychic  /  Focus Blast

Donphan @ Grassium Z  
Ability: Sturdy  
EVs: 252 Atk / 4 SpD / 252 Spe 
Jolly Nature  
- Seed Bomb  
- Ice Shard  
- Superpower  
- Earthquake  

Swampert @ Rindo Berry  
Ability: Torrent  
EVs: 160 SpA / 184 SpD / 164 Spe  
Calm Nature  
IVs: 0 Atk  
- Ice Beam  
- Yawn  
- Protect  
- Hydro Cannon

What they do:
Landorus-Therian: this is the main poke on the team. it lives 2 ice shards from Donphan and KOs back. Beats Zygarde, slow Mamoswine, and Torterra. If you run into something that I don't specifically mention, Lando-T probably beats it.

Donphan: beats Swampert and non-rindo berry mamoswine.
Swampert: Lives a 252+ z-grass knot from a Landorus-Incarnate (or therian) and can Yawn -> Protect. Lives 252+ Z-thousand arrows from Zygarde and can Yawn -> Protect.

This team struggles with:

Mamoswine @ Rindo Berry
Fast Rindo Berry Mamoswine with Freeze Dry for Swampert, Icicle Crash, and Ice Shard.