426 Drifblim

Hex is recommended for its fast energy generation, while Astonish is just a terrible move overall. 

Icy Wind has a decent damage profile and, more importantly, a 100% chance to drop the target's attack stat by 1 stage. This artificially boosts Drifblim's bulk and frequently forces switches or gives the next Pokemon on your team a great chance to come in with an advantage. Shadow Ball is noted for being one of the better attacks in the game due to its great neutral coverage and solid damage per energy rating, and works great in conjunction with Icy Wind, as the former can be used to bait shields easily. This is made especially effective when you consider the fact that Icy Wind's defense debuff ignores shields.

Drifblim is a great counter-pick to many, many huge threats in the tier. Its solid bulk and outstanding moveset allow it to threaten many opponents, and its access to a very quick Icy Wind allows it to act as one of the few "supportive" Pokemon in the game by forcing switches and softening up the opponent. Drifblim is a great Pokemon in the Great League, and should always be prepared for.

The level 50 update significantly improves Drifblim's performance in Ultra League, as its favorable typing and movesets allow it to perform well very consistently. Access to both Shadow Ball and Icy Wind allows Drifblim to hit pretty much everything in the meta for at least neutral damage, which means Drifblim will always have some play. Drifblim also notably has solid performances in both open Ultra League and Premier Cup, though Giratina is still more dominant with greater bulk and access to stronger Shadow Claw or Dragon Breath.

Drifblim's restricted CP and high competition for its niche leaves it high and dry in the Master League.