Chansey

Combined with Eviolite, Chansey's unfathomable Special Defense and HP allow her to wall some of the most powerful special attackers in the metagame. Eviolite bolsters Chansey's physical bulk to be quite good—comparable to that of the likes of Donphan—which truly separates her from Blissey and allows her to check Psyshock attackers such as Life Orb Adaptability Latias. Additionally, Chansey's grand HP stat generates very large Wishes, fundamentally allowing her to completely revitalize allies. As Chansey can switch in against many threats, she often receives opportunities to use Wish or Heal Bell and fulfill her role as an excellent cleric. Chansey's Normal typing grants her one immunity but also one weakness; however, Fighting-type attacks are very uncommon among special attackers, so it's a good typing for a special wall. Chansey's positive defensive qualities have made her a staple on stall teams; however, Chansey also has a few flaws dragging her down. Her terrible attacking stats limit her sources of damage to just Skill Swap (against Poison Heal Pokemon), Seismic Toss, and Toxic. As Chansey relies on her Eviolite to wall foes, Knock Off and Trick from the likes of Mew and Latios, as well as many other threats, can water down Chansey's walling ability for the rest of the match. Chansey is slow, and her only attacking move is Seismic Toss, so she's very vulnerable to Taunt, unless she is using Magic Bounce. Chansey is also very one-dimensionsal and extremely predictable; thus, it's easy for the opponent to bait a switch and gain free momentum against Chansey. However, even with these flaws, Chansey's ability to single-handedly check some of the metagame's most powerful special attackers, such as Mega Diancie, has made her the most pivotal wall for stall teams.