Hey Dank, cool team you have here. It does have some little problems though, let me explain:
Gengar is the largest threat (factoring in usage) to your team. Your best way of dealing with it is Metagross' Bullet Punch and Flygon locking himself into Outrage. Both let a Steel type set up easily (especially the latter). Substitute Gengar is even more troublesome, forcing you to Bullet Punch to break its sub, then Outrage with Flygon, letting Steel types set up and sweep your team. Another thing that can be troublesome, especially when paired with Substitute Gengar, is Tyranitar. Your best ways of dealing with it are (again) Metagross, Flygon and Gyarados in a pinch. However, the core of SubSplit Gengar and Choice Band Tyranitar destroys team, as both Metagross and Flygon are hit hard by Tyranitars boosted attacks, even when they resists it like Stone Edge and Crunch / Earthquake hits even harder.. You also have a slight Flygon / Dragonite weakness. Both of your Dragon resists are weak to Ground. This isn't too big of a problem because you have Flygon, but when he is down, DD Dragonite, for example, can sweep your team with ease.
The best way of dealing with all this is Scizor. It can Pursuit and Bullet Punch Gengar, while also taking little damage from its attacks. It also resists both of Stone Edge and Crunch and has good enough bulk to shake it off. It can then Bullet Punch / U-Turn Tyranitar for great amounts of damage. Finally, it resists Outrage and is neutral to Earthquake and can then Bullet Punch Flygon / Dragonite. Unfortunately, I can't find room for it on your team, as every team member is crucial to your teams success. The easiest way for fitting it onto your team, is by moving Celebi to the lead position and replacing Metagross with Scizor. Celebi makes for a great lead, and you still have the offensive power Celebi used to provide. The sets are:
Scizor @ Choice Band | Technician
Adamant | 248 HP / 252 Atk / 8 Spe
Bullet Punch / U-Turn / Superpower / Pursuit
Celebi @ Leftovers | Natural Cure
Timid | 40 HP / 252 SpA / 216 Spe
Stealth Rock / Leaf Storm / Earth Power / U-Turn
The Celebi set can be modified slightly to your likings. You can replace Leftovers with Occa Berry to set up SR against Infernape and Dragonite leads and defeat Heatran leads, but you lose out on the survivability. You can also replace U-Turn by Hidden Power Ice to beat Gliscor and Dragonite (if you have Occa Berry) or Hidden Power Fire to beat Forretress, Scizor and Skarmory.
Another solution that keeps the team more like the original version is replacing Metagross with Bronzong. It defeats Gengar pretty handily, easily surviving its attacks, and KOing back with Gyro Ball. It also beats Choice Tyranitar, resisting Stone Edge and Earthquake, and doing great damage back with Gyro Ball. Lastly it resists Dragon and is immune to Ground, and OHKOs and 2HKOs Flygon and Dragonite back with Gyro Ball, respectively.
Bronzong @ Leftovers | Levitate
Sassy | 252 HP / 84 Atk / 80 Def / 92 SpD
Stealth Rock / Gyro Ball / Earthquake / Explosion
Good luck with the team!
