The number of Pokémon caught during Pokémon GO Fest by members of Team Mystic, Team Instinct and Team Valor were tallied up, and the team that caught the most Pokémon determined which of the three Pokémon is appearing first. And the winner was Team Mystic, which means the Legendary Pokémon Articuno is now appearing in Raid Battles across the globe. Now everyone can catch Articuno, but it will appear at Gyms only for a brief while, so join your friends and try to defeat this Pokémon right when you get a chance. The other two Legendary Pokémon of the trio, Zapdos and Moltres, will soon show up at Gyms for you to challenge.
Articuno appears at Pokémon GO Gyms only for a “brief while”
Pokémon Blog 