Lapras

Lapras's STAB Blizzard and tremendous bulk give it positive matchups against many of the physical attackers of Ubers, namely Swords Dance Mew, Tauros, and Snorlax. Its Speed is just enough to outrun Chansey and Exeggutor, which it can potentially threaten with Sing, disrupting common sleep strategies. Because Lapras is so hard to wall as a result of BoltBeam coverage, absorbing its Sing with paralyzed Pokemon is also very difficult; it can blow past Pokemon like Alakazam and Starmie easily when they're paralyzed. Furthermore, Lapras is generally not concerned with taking paralysis itself, and when it's paralyzed it can potentially switch in on sleep moves from Pokemon like Exeggutor and threaten massive damage thereafter. Lapras's quadruple resistance to Ice and immunity to freeze lets it switch into certain Ice-type moves, notably against Chansey, softening a somewhat common Mewtwo removal strategy. Lapras's ability to trade hits favorably against almost the entirety of Kanto's finest allows it to clear the way for even stronger allies, positioning them for a quick beatdown.

However, Lapras's lack of reliability comes back to bite it very frequently. It's easily worn down over the course of a game, as its Speed often forces it to take a hit before it can make a move, and it crucially lacks reliable recovery. Being weak to Thunderbolt and neutral to Psychic doesn't help it either, and an untimely critical hit can significantly limit the impact it will have over the course of a game. Additionally, Lapras faces stiff Water-type competition in Cloyster and Starmie. Both are faster than Lapras, and Cloyster has access to Clamp and Explosion, while Starmie has Recover and Thunder Wave. While they can't replicate its power or Sing access, they usually bring more consistent utility to a team, which often pushes Lapras out during teambuilding.