Blissey

Blissey is a solid special wall thanks to its gargantuan HP and good Special Defense, allowing it to tank almost any special attack. This special bulk allows Blissey to forgo Ice Scales for abilities like Magic Guard and Regenerator that give it extra survivability against all forms of chip damage. Its low Attack also lets it deny Strength Sap's healing from most special attackers like Miraidon and Arceus-Fairy. Blissey has the fatal flaw of having nonexistent Defense, so it is forced out by physical attackers; however, this can also be used to your advantage to offensively Imposter-proof Blissey with said attackers. Blissey faces competition from Chansey as a Magic Guard user because of Chansey's increased bulk from Eviolite; however, Blissey has the advantage of not being deterred as much by Knock Off. Additionally, Blissey is quite passive, especially against Regenerator users, so it can struggle to progress the game apart from slow pivoting.