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Wartortle to Blastoise doesn't even make sense.
Charmeleon is halfway between Charmander and Charizard, to the point of having one horn and developed claws.
Ivysaur is halfway between Bulbasaur and Venusaur with the flower about to bloom and the teeth.
Wartortle further develops Squirtle's tail and has winged ears, then suddenly Blastoise has different ears, a much different tail, different feet, white underbelly and a cannon motif which didn't exist. He's dramatically different unlike the other two.