I think a set like this is what Forrest is aiming for:
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MixNite - Dragonite
Item: Life Orb
Nature: Rash
EVs: 112 Atk / 200 SpA / 196 Spe
Moveset
~ Superpower
~ Draco Meteor
~ Fire Blast / Flamethrower
~ Roost / Thunderbolt
Mixed Dragonite functions extremely similarly to Mixed Salamence. While Salamence generally has the advantage when it comes to using this set because of its higher Special Attack and Intimidate, Dragonite's unique access to Superpower, along with higher defenses overall, make him a worthy candidate.
With a Rash nature and 112 Attack EVs, Dragonite is guaranteed to OHKO 0 HP / 252 Def Bold Blissey, 252 HP Tyranitar, and 4 HP Heatran after Stealth Rock damage. Salamence must rely on Brick Break to combat all three of them, while none of which are OHKOed, which again emphasizes the advantage of using MixNite over MixMence. Draco Meteor is a powerful STAB attack and can deal massive damage to Hippowdon, Swampert, and other pokemon expecting a physical attack. A fire move in the third slot complements this set for universal coverage and prevents Skarmory and Bronzong from walling Dragonite entirely. Roost is the preferred option to recover Life Orb and Stealth Rock damage; however, Thunderbolt is useful option to combat bulky Water-type Pokemon, most notably Gyarados and Suicune.
As previously stated, the given Attack EVs are necessary to OHKO Bold Blissey, Tyranitar, and Heatran. 196 Speed EVs place Dragonite at 245 Speed, enough to outrun Jolly Tyranitar and just about any defensive Celebi and Zapdos, and the remaining EVs are placed in Special Attack.
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Yachi Berry as an equipped item lowers weakness to ice.