While Porygon is unlikely to ever come back in the Pokemon anime, the virtual Pokemon is still an ever-present figure in the games, as well as its evolutions. Here is how you can get the Upgrade and Dubious Disc items to evolve it.
How to Evolve Porygon in Pokemon Scarlet & Violet
Porygon will evolve to Porygon2 when it’s traded while holding the Upgrade item, while its second form evolves to Porygon-Z when it’s traded holding a Dubious Disc. Both of these can be easily obtained while going through the Indigo Disk DLC, but you’ll still need someone to trade Porygon with.
Where to Get Upgrade in Pokemon Scarlet & Violet
Upgrade is obtained by catching 100 Pokemon in the Blueberry Pokedex. You can claim it by opening the general Pokedex, heading to the Blueberry tab, and pressing X to get your items. You can only claim one Upgrade through this method.
Alternatively, you can buy Upgrade from the School Store in the Blueberry Academy for 250 BP. Since there’s a lot of other important stuff you need to use BP for, getting the free one from the Dex is the best choice if you just need its entry.
Where to Get the Dubious Disc in Pokemon Scarlet & Violet
Similarly, Dubious Disc is the reward for catching 110 Pokemon in Blueberry Pokedex. And if you ever need more of it, the School Store in Blueberry Academy is also selling it for 250 BP at all times.
If you’re trading for evolving Porygon with someone, don’t forget to give Porygon2 the Dubious Disc before trading it again or it’ll just make you lose some extra trading time, which is just mildly annoying but still an inconvenience.
If you lost your Upgrade/Dubious Disc or want to evolve a new Porygon, you’ll have to grind some extra BP for that. Fortunately, there are plenty of forms of doing so in the game.