While most Pokemon evolve by reaching a certain level or being exposed to a specific elemental stone, there have always been some fascinating exceptions to the rule. Way back in Gen 1, you could only get Gengar or Machamp by trading a Haunter or Machoke, respectively.
This idea was further developed in Gen 2 when Steelix and Scizor came from traded Onix and Scyther holding a Metal Coat. As the generations went on, more and more niche clauses were introduced in order to make completing your
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