Here is a team that I built around mega gyarados, I got top 10 on the ladder with it and ended up with 23 wins and 3 losses.
https://pokepast.es/13b2987f0ae443ea
Gyarados-Mega @ Gyaradosite
Ability: Mold Breaker
Level: 50
Jolly Nature
- Crunch
- Waterfall
- Earthquake
- Substitute
Gyarados is a really good lead because it beats almost all stealth rock setters and it removes its rock weakness. Waterfall is for aero/rhydon/nidos and it allowes it to beat common rockers putting you in a 6-5 lead (everyone always suicide rocks). Crunch lets you hit psychics like mew/slowbro/starmie/alakazam for maximum damage. Earthquake is needed for doing about 45% to melmetal and hitting muk for more damage. Sub lets you take advantage of the status spam in this meta. Jolly is needed to outspeed venu/eevee/nidoqueen. There is no switchins to gyarados so take advantage of that.
Eevee-Starter
Ability: Run Away
Level: 50
Jolly Nature
- Sizzly Slide
- Sappy Seed
- Sparkly Swirl
- Protect
Eevee is the only cleric in the meta, so its basically a given on every team except HO. This set is standard and there is nothing special about it. Eevee is the primary switchin to defensive mew on this team and it helps wake up melmetal.
Nidoqueen
Ability: Poison Point
Level: 50
Jolly Nature
- Earthquake
- Super Fang
- Ice Punch
- Stealth Rock
Nidoqueen was the best rocker for this team as it synergizes so well with gyarados. Nido helps hardwall zapdos and check melmetal and fighters. Earthquake + superfang guarantees to take away half hp of every mon because all ghosts are weak to eq. Ice punch does the most damage to zapdos and jolly is for outspeeding eevee and non speed nature gyarados and venusaur. You almost never want to lead nido and want to use it as a reactionary mon, be careful for uturns on zap.
Mew
Ability: Synchronize
Level: 50
Timid Nature
- Roost
- Will-O-Wisp
- Psychic
- Dragon Tail
Mew is another mon that is needed on every team. This set is fairly standard with willo allowing it to beat muk and melmetal, dtail preventing sweepers like cm alakazam, and psychic for stab that hit everything else hard.
Melmetal
Ability: Iron Fist
Level: 50
Adamant Nature
- Double Iron Bash
- Thunder Wave
- Earthquake
- Rest
Melmetal yet again another mon required on every team. This set is standard, double iron bash/eq hits about everything in the tier really hard and twave can punish switches and allow melmetal to flinch hax. Last slot can be rest or icepunch if you want to hit zapdos harder. Melmetal checks about everything in the tier and you should try to save it for late game when zapdos is gone.
Zapdos
Ability: Pressure
Level: 50
Timid Nature
IVs: 0 Atk
- Roost
- Toxic
- Substitute
- Thunderbolt
Finally zapdos was chosen in the last slot. Sub toxic is really good as it lets it beat things like rhydon and setup a sub for free against eevee. It also has a good matchup vs other zapdos and mew. The con is it is completely walled by nidos and is worse against venusaur. Zapdos is also a nice check for melmetal which gives every team problems.