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Gen II as a whole. It was so bad that most trainers use Kanto pokémon.
Stantler was found only in that grass before Ecruteak, and in the very next route you could find the much better Tauros or Miltank.
Snubbull was one of the 1% spawn rate and it was only available into one route.
Qwilfish was only used by early game fishermen (later on they'd use almost exclusively Gyarados).
Hoppip was impossible to train early on because it had no offensive moves.
Ledyba was only found with early bug catchers and other than spamming Supersonic they could do nothing.
There was Mantine, but who the hell would pick it over a Starmie or Lanturn?
Then there's the likes of Sneasel or Gligar who would be completely forgotten if it wasn't for Gen IV giving them new evolutions.