
While Serperior is generally agreed to often be an annoying Pokémon to face, it was also agreed by the majority of council to not be broken or worthy of a ban.
Serp is adept at forcing progress with Glare, backed by spammable snowballing Contrary Leaf Storms, a great speed stat, and good longevity to boot with Leech Seed. However, Grass also has many notable resists in the tier, including Gholdengo, Corviknight, Pecharunt, Trevenant, Salamence, Moltres and Goodra-H, so players are not hard pressed to prepare for it in the builder.
Serperior is easily forced out from behind its Substitutes by using slower U-Turns, which also removes Leech Seed. There also exist other options to force it out from behind a Sub including Roar, Curse, Infiltrator Dragapult (who outspeeds it) as well as Icicle Spear Kyurem or Toxtricity.
Furthermore, the limited PP of Leaf Storm is also quite exploitable by Unaware mons such as Unaware Clefable and Pressure Zapdos.
All these factors to combine to make Serperior a strong, but manageable, tier menace.