Gyarados @ Flyinium Z  
Ability: Intimidate  
Level: 50  
EVs: 36 HP / 252 Atk / 4 Def / 4 SpD / 212 Spe  
Adamant Nature  
- Waterfall  
- Dragon Dance  
- Bounce  
- Earthquake/Substitute/Taunt/Ice Fang
Standard Fly-Z set. The speed stat allows you to outspeed greninja at +1, the rest dumped in bulk. The last move can be a variety of moves depending on what the team needs.

Gyarados @ Rockium Z
Ability: Intimidate  
Level: 50  
EVs: 252 Atk / 4 SpD / 252 Spe  
Jolly Nature  
- Waterfall  
- Dragon Dance  
- Stone Edge  
- Earthquake/Substitute/Taunt/Ice Fang
Similar set, I've put the Rockium-Z here which is another major option, last move up to grabs. Max speed is needed to outspeed base 80s like Mamoswine.

Gyarados @ Figy Berry  
Ability: Intimidate  
Level: 50  
EVs: 236 HP / 4 Atk / 252 Def / 4 SpD / 12 Spe  
Impish Nature  
- Waterfall  
- Ice Fang  
- Roar  
- Toxic / Taunt 
A defensive set with bulky berry can be used as a disruptor and wall to certain threats like mega salamence and some blaziken variants whilst having a decent lando/hippo matchup, the speed evs are for speed creeping tho max max is fine.