There is one Pokémon that is weaker than all of the rest, due to a mixture of its poor stats and an abysmal move pool. The Pokémon franchise has had weak Pokémon since the beginning, with Magikarp’s entire gimmick in Pokémon Red & Blue being that it’s useless until it evolves, which only prompted fans into using it to defeat the Elite Four of Kanto.
Magikarp was the first in a series of Pokémon whose gimmick was tied to weakness, with Feebas from Pokémon Ruby & Sapphire being similar in many ways. It takes more than just bad stats for a Pokémon to be weak, as it needs a terrible move pool or an ability that inhibits its combat abilities. A Pokémon like Smeargle has terrible stats, but its exclusive access to Sketch gives it one of the best move pools in the franchise, allowing it to throw Dark Void and Sacred Fire right into the faces of enemy Pokémon. Similarly, Wishiwashi has horrible stats, but its Schooling ability allows it to transform into a much stronger Pokémon.
There is one Pokémon that is definitively weaker than the rest of the creatures in the series. What makes the identity of this Pokémon so surprising is that it’s actually a Legendary Pokémon that debuted in the Alola region. Legendary Pokémon are the most powerful creatures in each game, with stats that allow them to walk over the teams of the best trainers in the series, but there is one among them that can’t even stand up to Magikarp.
The weakest Pokémon in the series is Cosmog from Pokémon Sun & Moon. It has the lowest base stat total of any Legendary Pokémon in the series, but there are Pokémon with weaker stats out there. The main difference comes down to moves. Pokémon like Sunkern, Blipbug, Caterpie, and Weedle have weaker stats, but they can learn moves that are useful. Cosmog can only ever learn two moves: Splash and Teleport. Splash is the former signature move of Magikarp and it cannot harm enemies, while Teleport has no effect in trainer battles, as its main use is escaping from wild Pokémon.
Cosmog can evolve into some powerful Legendaries, as it’s the first stage of the two box mascots for Pokémon Sun & Moon. When viewed in a bubble, though, it’s arguably the worst Pokémon in the series. Even a lowly Farfetch’d could take down a Cosmog, as it’s a Pokémon that’s unable to defend itself in battle, and is only good for running away.