Red's Gym Badges triggered a fusion machine and created this Pokémon. Team Rocket stole an Eevee in order to research the EeveelutionsVaporeon, Jolteon, and Flareon, which was a mere beta-test for this creature. It nearly destroyed Saffron City. Red, Blue, and Green all did battle with the beast and after a long battle, managed to defeat it. After being defeated, the three legendary birds separated to their original forms and left.
A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.
Trivia
In Pokémon Adventures canon, it never had a proper name. However, Coronis coined the term Zapmolcuno, a portmanteau of the legendary birds' names. Japanese fans also coined the term サ・ファイ・ザーSa Fai Zaa, a combination of the legendary birds' Japanese names Thunder, Fire, and Freezer.