Now that everyone is acquainted with Pokemon GO, or at least the screen that informs players that the servers are down, some people are beginning to ask deeper questions about the game. While most fans know that Pokemon GO only features Pokemon from the original two Pokemon games (for now), some fans have pointed out that four very important Pokemon are missing: namely the Legendary Pokemon.
Outside of some anecdotal (and doubtful) accounts on Twitter, no one has seen or caught Articuno, Moltres, Zapdos and Mewtwo in Pokemon GO. We know that Niantic didn't forget about these Pokemon, since the Legendary Birds appear as the logos for the three teams in Pokemon GO: Team Instinct, Team Mystic and Team Valor, but their absence in the game suggests Niantic Labs (the developer of Pokemon GO) might be hiding them for a bigger purpose.
Fans of Niantic Labs' other game, Ingress, probably have a clue about why the Legendary Pokemon haven't appeared yet. Niantic occasionally organizes large citywide events for Ingress players, in which players from different teams jockey for control of cities. It's likely that Niantic has plans to incorporate the Legendary Pokemon into these large events, to encourage players to work together.
We saw a hint of this in Nintendo's first trailer for Pokemon GO, when hundreds of players gathered in Times Square to fight a Mewtwo. After delivering a final blow seconds before a countdown was set to expire, Mewtwo appeared in all of the players' games, a reward similar to the events seen in regular Pokemon games.
Of course, as each team has a Legendary Pokemon as their mascot, it's possible that players will have to compete within their team for a chance at one of the Legendary Birds. We haven't seen any scoring systems yet, but it's always possible that Niantic could hold some sort of intra-team competition for a Legendary Bird. Pokemon Shuffle, another Pokemon themed mobile game, holds regular ranked events with various items and Pokemon given out to top players. Niantic hasn't traditionally gone that route with events, so take that theory with a grain of salt.
Once Niantic sorts through their unfortunate server issues and releases Pokemon GO to the rest of the world, expect to hear some additional details about how to catch Legendary Pokemon in the game These likely will be regional events, so be prepared to travel if you want to get your hands on these extra-rare Pokemon.