Lugia

By virtue of its behemoth bulk, access to Recover, and Flying typing which grants it a Spikes immunity, Lugia is the bulkiest Pokemon in GSC Ubers. 106 / 130 physical bulk allows Lugia to switch into almost every physical attacker and, paired with Curse and Whirlwind, beat them one-on-one. This makes Lugia a very valuable defensive piece for a lot of teams that can also work as a potential wincon. Its monstruous Special Defense also lets it avoid the 2HKO from every non-STAB Thunder, meaning only Pokemon like Zapdos and Jolteon can consistently 2HKO it with unboosted attacks. Lugia can even run moves like Surf and Toxic to turn the tables on Pokemon that usually give it trouble, like Golem, Steelix, and Rhydon, while supporting its team.

However, Lugia struggles to deal meaningful damage until it gets going with Curse boosts. Furthermore, Lugia's strongest attack is Aeroblast, which has only 8 PP, so it can get stalled very easily by smart pivoting, restricting Lugia to only phazing foes until it can safely start attacking. Lastly, Lugia's inability to get past metagame beasts like Zapdos and Tyranitar limits its utility for the majority of the early- or mid-game to acting as a phazer and soft counter to physical attackers.