Pokemon has a habit of introducing new evolutions for older Pokemon in new generations. One example is Porygon, who obtained a second evolution in generation 2's Pokemon Gold/Silver.
Then, when Pokemon Diamond/Pearl was announced, Porygon2 could evolve into Porygon-Z. Fortunately for some trainers, the methods of evolving Porygon and Porygon2 haven't changed over the years.
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