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Gyarados @ Cheri Berry
Ability: Intimidate
EVs: 4 Def / 252 Atk / 252 Spe
Jolly Nature
- Dragon Dance
- Natural Gift
- Bounce
- Waterfall
Tyranitar @ Tyranitarite
Ability: Sand Stream
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Dragon Dance
- Stone Edge
- Crunch
- Ice Punch
Mega Tyranitar is a bit uncommon. Because of this, people usually think Gyara is the mega when both are on the same team. This helps Gyara lure in Ferrothorn easier with Natural Gift, and keeps the other person guessing until the necessary info is revealed. Aside from luring Ferro, Cheri Berry also cures paralysis, meaning something like Thundurus-I can't stop your sweep. Mega Tar is now free to use something other than Fire Punch for coverage, like Ice Punch or Thunder Punch to catch bulky Garchomp or Keldeo respectively.
They form a good offensive duo. They do a nice job of setting up on each others checks and counters. For example, Gyara is threatened by Raikou, Mega Manectric, CB Talonflame, and Kyurem-B. Mega Tar DDs on them all easily, and proceeds to threaten the opposing team. Mega Tar is threatened by ground types, such as Landorus-T and Hippowdon. Scizor, Keldeo, Conkeldurr, and Excadrill are also troublesome. Gyara threatens and sets up on the majority of these relatively well, making it a good partner. Intimidate can also ease Mega Tar's set up in some situations.
In addition to all of this, both pressure and weaken each others checks and counters. Skarmory is going to be weakened by one of Gyarados or Mega Tyranitar at +1, letting the other finish the job afterwards. This is especially true because most Skarmory are special defensive now. Clefable and Azumarill are common checks to this core, and can also be weakened enough for one member to pick off later. Rotom-W is a threat to this core, but if Mega Tyranitar has +1 prior to it coming in, Stone Edge is taking it down to a point where it can't handle Gyarados.