After playing with the same core for 3 years and peaking number one in different metas, I think it's safe to say this is a good core:
Dragonite (F) @ Lum Berry
Trait: Multi Scale
EVs: 4 HP / 252 Atk / 252 Spd
Adamant Nature (+Atk, -SAtk)
- Dragon Dance
- Fire Punch
- Extreme Speed
- Outrage
Scizor (F) @ Life Orb
Trait: Technician
EVs: 4 HP / 252 Atk / 252 Spd
Adamant (+Atk, -SAtk)
- Bullet Punch
- Swords Dance
- Super Power
- Bug Bite
Breloom (F) @ Focus Sash
Trait: Technician
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Spore
- Swords Dance
- Mach Punch
- Bullet Seed
Starmie (F) @ Life Orb/Left Overs
Trait: Analytic/Nature Cure
EVs: 4 HP / 252 SpA / 252 Spd
Timid Nature (+Spd, -Atk)
- Rapid Spin
- Rain Dance/Ice Beam/ T-Bolt
- Scald/Surf/Hydro Pump
- Psychic/Psyshock
Breloom sets up on hazard setters, puts switching sweepers to sleep, and does a number on 4 out 5 weather starters, and can handle Starmies problems. Starmie spins away hazards, changes weather if must, kills most of the spin blockers in one or two hits and ensures Dragonite can sweep. Scizor sets up on choice locked pokemon and wears anything that outspeeds Dragonite after DD and proceeds to OHKO and 2HKO most of the meta after SD + LO, while Dragonite sets up on Scizors most loathed enemy, fire pokemon and with nearly perfect coverage and +2 priority proceed to demolish the enemies team.
The last 2 slots can be customized to do nearly anything from DragMag to Rain Offense, etc.