Since the game went online over a year ago, players of Niantic’s massively popular (and often frustrating) AR monster-catcher have wondered where all the legendary creatures are hiding in Pokémon Go. The original Game Boy title had massively powerful, interesting, and unique legendary Pokémon way back in the 90s, but the smartphone game launched without access to Articuno, Zapdos, Moltres, and Mewtwo, despite a heavy feature in the original trailer.
Source: How-To Geek
