"Dennō Senshi Porygon" (Japanese: でんのうせんしポリゴン, Hepburn: Dennō Senshi Porigon, translated as "Computer Warrior Porygon," most often known as "Electric Soldier Porygon") is the 38th episode of the Pokémon anime's first season. It aired only once in Japan on December 16, 1997.
In the episode, Ash and his friends find out that there is something wrong with the Poké Ball transmitting device at the Pokémon Center. They must go inside the machine to find out what is wrong.
The episode is controversial because it had a lot of flashing lights that caused epileptic seizures in hundreds of Japanese viewers. More than 600 children in Japan went to hospitals as a result. People in Japan call this the "Pokémon Shock" (ポケモンショック, Pokemon Shokku). After this, the episode was banned and the Pokémon anime was paused for four months.