Zygarde (Complete Forme)

Great League: X / 5

At this moment in time, Zygarde cannot be traded. However, if it does become tradable (and it probably will; Zygarde is a Legendary, not a Mythical), a Great League Zygarde-C can be obtained. In the event that happens, this form of Zygarde is an absolute menace, boasting a stat product that is comparable to well-established tanks such as Lickitung and Azumarill. Though its moveset can be rather slow, Zygarde-C's insane bulk easily makes up this setback and can overwhelm most things that cannot hit it super effectively. Being a Dragon-type that can threaten Steel-types and Carbink is a useful quality, making Zygarde-C a difficult Pokemon to wall. Beware of Fairy- and Ice-type Pokemon, however.

Ultra League: 4.5 / 5

Much like in Great League, Zygarde-C continues to possess insane bulk in the Ultra League - enough to tower over even Giratina. It possesses the tools to dismantle some of Ultra League's finest tanks - Earthquake keeps Registeel and Galarian Stunfisk at bay, Crunch can make Cresselia think twice before about challenging it, and its STAB Dragon Tails (and Crunch, again) can topple over Giratina. To illustrate Zygarde-C's tankiness, it is bulky enough to cleanly avoid getting 2HKOed by Cresselia's Moonblast after some Psycho Cut chip, something that Giratina struggles with. All in all, Zygarde-C is poised to become a metagame-defining threat the moment that a player successfully collects the Cells necessary to transform it. That said, this beast still deeply struggles against Fairy- and Ice-type Pokemon, so Pokemon such as Tapu Fini, Walrein, Alolan Sandslash, and Alolan Ninetales are key to defeating it safely.

Master League: 5 / 5

No Pokemon reigns over multiple leagues in the same way that Zygarde-C can (you tried, Dragonite. I commend your efforts!), and Master League is actually its strongest league. It kicks Lugia off its long-held throne of having the highest stat product in the game and boasts even greater tankiness. It overpowers every other Dragon-type in the game (sans Dialga due to its Steel typing) in a Fast Attack faceoff; this includes the future titans Kyurem-B/W and Eternatus. It can facetank Mewtwo's Ice Beam with health to spare, and can even survive Dialga's Draco Meteor. Thanks to Crunch and STAB Earthquake, Zygarde-C also possesses the tools to go toe to toe against Lugia and Dialga respectively, two common countermeasures against other Dragon-type Pokemon.

So what safely contains this monarch's overwhelming power? Fairies once again come the rescue! Zygarde-C dreads Togekiss the most, as its entire moveset (save for the extremely sluggish Hyper Beam) is completely walled. Togekiss can easily Charm down a full HP Zygarde-C without ever throwing a Charged Attack. Play Rough Zacian and Xerneas can defeat Zygarde-C fairly reliably, but they can take significant damage from Earthquake. Mamoswine can make short work of Zygarde-C with its doubly-effective Avalanches.