Voltorb and Foongus will be appearing throughout Paldea as part of this Mass Outbreak event, along with one " mystery Pokémon" that can't normally be encountered in Paldea. Going from the small parts of the Pokémon not obscured in the promotional image, this "mystery Pokémon" may be Voltorb's Hisuian form. Pokémon encountered in these Mass Outbreaks are more likely to be shiny than those typically encountered in the wild.
To participate in these mass outbreak events, players will need to download and install the latest update data; and to download the latest Poké Portal News. If players have connected their Nintendo Switch system to the internet while playing Pokémon Scarlet or Violet, this should happen automatically. Players can also manually download the Poké Portal News by selecting Poké Portal from the X menu, and then selecting Mystery Gift, and then Check Poké Portal News. A paid Nintendo Switch Online membership is not required.
- Sources
Prepare for Mass Outbreaks of...Poké Balls?!
sv-news.pokemon.co.jp