Blissey

Blissey's enormous base 255 HP and large base 135 Special Defense stats just scream special wall; in fact, it has the most special bulk in the game and access to instant recovery in Soft-Boiled. Blissey is so bulky that even extremely strong or boosting special attackers such as Choice Specs Heatran, Choice Specs Latias, Choice Specs Kingdra in rain, Gengar, Starmie, offensive Calm Mind Jirachi, offensive Calm Mind Suicune, and Substitute + Petaya Berry Empoleon are unable to break through it. This walling prowess allows it to spread status effectively via Thunder Wave and Toxic or take advantage of its huge support movepool with options such as Stealth Rock, Heal Bell, and Wish. Despite its lopsided stat distribution, it has more physical bulk than Clefable when fully invested and can spread status to physical attackers such as Tyranitar and Gyarados that cannot OHKO it.

Blissey has been usurped by Clefable as a special wall due to Blissey's massive weakness to residual damage. Clefable's immunity to this residual damage and access to more utility moves such as Knock Off and Encore largely outclass Blissey's astronomical bulk. Blissey's vulnerability to all three entry hazards, sand, and status compromise its bulk and wear it down quickly. Blissey especially struggles with offensive pressure from attackers such as Breloom, mixed Flygon, and Tyranitar when backed by Spikes, forcing either Rapid Spin support or another way to mitigate entry hazards. Blissey also can easily be taken advantage of via Trick, Explosion, Taunt, Ghost-types with Substitute, and Lum Berry, as its offensive options are very weak and it can't afford to be locked into one attack. Blissey despises Fighting-types, as Machamp, Breloom, Infernape, and Lucario all OHKO it after Stealth Rock and force it out. Fighting-type coverage also is very common and attackers such Tyranitar, Dragonite, and Scizor can devastate it with Superpower. Blissey does not enjoy repeatedly dealing with physical attackers such as Gyarados, Metagross, and Swampert, especially if they can mitigate status.