Blissey

Blissey is the defining special wall of ADV OU. It has no special weaknesses and shrugs off special attacks with impunity, countering a wide range of special threats and minimally acting as a safe pivot into those that run utility moves to get past it. Because it takes so little damage, it can choose not to recover after taking a hit even under sand or after taking Spikes damage, generating free turns that can be used to gain momentum via its punishing moves or double switches. Its moveset can be customized to suit both defensive and offensive needs; it can apply three different kinds of status, support teammates with Wish or Heal Bell, fire off punishing elemental coverage moves, and even pull off a surprise Counter in the face of a physical threat. Due to its enormous HP stat, Blissey can also deal with a number of physical moves from mixed attackers like Salamence, Zapdos, and even mixed Tyranitar or defensive Swampert to some extent.

Blissey's main weaknesses are its lack of resilience against powerful physical moves and relative passivity. This makes it easy for Metagross, physical Tyranitar, and Snorlax to exert pressure on Blissey and for Calm Mind users, especially those with a healing move, to overwhelm Blissey with boosted special attacks. Blissey can also be forced out by status and is easy to set Spikes against. Still, many of these weaknesses can be patched by the appropriate filler moves. Blissey on non-Spikes teams usually carries Wish and is ideal for supporting bulky wallbreakers like Choice Band Salamence, Metagross, and Suicune.

Blissey is mostly used with Spikes, and it is especially resilient in the face of Spikes and sand compared to other special tanks like Celebi, Snorlax, and Regice. It is by far the most commonly used special wall in the Toxic + Spikes + Sandstorm (TSS) archetype. However, it can also be used without Spikes to shield and support a late-game setup sweeper like Curse Snorlax or Calm Mind Jirachi. Blissey can also be used on non-Spikes offensive teams as a robust special wall and one of the few Gengar checks.