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I'm surprised nobody brought this up, but that first design isn't really Ivysaur. There's a couple unusual cases in the internal index where Pokemon were replaced with their pre-evolutions while the sprites were moved to a different slot. Why? I don't fucking know, was editing the sprites that hard? Was the person who was working on those specific Pokemon retarded? We just don't know. Regardless, in this case that sprite is Venusaur, as can be seen in this sprite from Green version. The only other blatant example is Shellder and Cloyster (we know it from the same part of the Capsule Monsters pitch), but based on how Sugimori talks about Magnemite and Magneton a similar switch almost certainly happened. According to the back sprites from the source leak, some other shuffling was happening as well, like an alternate Nido back of some sort and yet another Magnesprite taking up another space, these are some weird outliers honestly.