Dragonite is not viable at all in Gen 8 AG. This is because there are better options for a Dragon Dance sweeper such as Zygarde, Necrozma-DM, etc. All these have better stats that make them more viable than Dragonite. Zygarde and Necrozma-DM are S-rank, while Dragonite is unranked in the AG Viability Rankings.
If you still insist on using Dragonite, I would suggest that you should use it in a tier that it's actually usable and viable. For example, in SS OU and SS Monotype. Dragonite is A-rank in Gen 8 OU and B-rank in Gen 8 Monotype. This is far better than in AG, where it can't keep up with the firepower offered by other Dragon-types.
Gen 8 OU
Dragonite @ Heavy-Duty Boots
Ability: Multiscale
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Dragon Dance
- Earthquake
- Dual Wingbeat
- Roost
Gen 8 Monotype
Dragonite @ Heavy-Duty Boots
Ability: Multiscale
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Dragon Dance
- Outrage
- Extreme Speed
- Earthquake / Fire Punch
Earthquake is generally better in OU because without that, you'd be walled by common Pokemon such as Heatran, Toxapex, Tyranitar, etc. While Fire Punch could also be used to hit the omnipresent Corviknight, it is very weak and fails to 2HKO Corviknight at +1 with Leftovers at full HP. Also, instead of Extreme Speed and Outrage you can use Roost, which allows Dragonite to get back to full HP for re-activating Multiscale.
However in Monotype, you can use Fire Punch as:
Outrage is its strongest STAB attack, dealing massive damage to anything that doesn't resist it. It should be used carefully, as it locks Dragonite in for a few turns. Extreme Speed allows Dragonite to pick off weakened Pokemon without taking damage and deal with fast threats such as Weavile and Tapu Koko. Earthquake hits Steel-types that resist its other moves such as Heatran, Aegislash, and Melmetal. Alternatively, Fire Punch can be used to hit Celesteela and Ferrothorn.
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