Fans of the original Pokémon games will remember the late game search for its rarest creatures, from the Legendary flying trio Articuno, Zapdos, Moltres, to the last two Pokédex entries Mewtwo and Mew.
To date, no one has been able to locate them within Pokemon Go (though one has appeared, perhaps unofficially) but the good news is that they have been teased to appear in the game in some form; developer Niantic confirmed at its Pokemon Go San Diego Comic Con panel that Legendaries are indeed on the way, but there have been clues in the game, too...
How we know Legendary Pokémon Mewtwo, Mew, Articuno, Zapdos and Moltres are in Pokémon Go
NesstendoYT on YouTube has been digging through the game's files to discover that the above Pokémon are indeed listed in the game:
Their absence in the game so far has led to questions of where - and when - they will appear. While it's still possible they could be found in the wild at a high enough Trainer level, one of these Legendary Pokémon - Mewtwo - was the focus of one of the game's first trailers, showing crowds of people teaming up to fight it, whittling down its health as a timer ticks down before capturing the Pokémon in a packed Times Square, suggesting that Mewtwo and other Legendaries could be unlocked through public events rather than random encounters.
Other datamining efforts have revealed not only the stats of each Legendary Pokémon - showing they are among the Best Pokémon in Pokémon Go, with Mewtwo having a staggering base attack of 284 against the current highest Dragonite with 250 - and that they also have no capture rate at all.
This suggests that they will be captured differently to other creatures in the game. If we use the trailer as a basis for how it could work, it might mean you'll get the Legendary automatically after you complete a certain task, such as everyone lowering their HP in a public space.
This is all certainly in developer Niantic's wheelhouse, as its previous game Ingress - on which Pokémon Go's map data is based on - has hosted special events range named 'Anomalies', which has teams compete over specific locations across the globe over the course of several weeks.
Participating players received an exclusive emblem for taking part, and the outcome of the event changed the course of the Ingress story.
While the developer has yet to fully announce anything along these lines for Pokémon Go, in 2015 Niantic CEO John Hanke told VentureBeat "given the success we've had with Ingress [events], it's a pretty safe bet".
The first Legendary Pokémon spotted in Pokémon Go - but how did it appear?
In early August, a player topped a Gym in Ohio with an Articuno, which is said to be the first Legendary appearance in the game. Multiple players verified the sighting, but how the player got the creature is in question. The owner claimed she received the Pokémon as part of an apology from developer Niantic after contacting them via email about an issue, and while it sounds possible, it's unlikely, as there has been no suggestion that Legendaries would be given away in this manner.
Other possibilities could be an exploit that has edited the creature's data to appear in the game, an error that has seen one spawn accidentally, or a glitch turn another Pokemon into the famed Legendary, similar to a case reported by a user who had their wild Caterpie transform into a Charizard once in their possession.
As such, players are still suggesting we'll have to keep waiting until a Niantic-run event or other activity before we can officially get Legendaries in our hands.
Want more help with Pokémon Go? Read our Pokémon Go tips, tricks, cheats and guides for insights on how to improve your skills, how to choose your Eevee evolution, and how CP works. Plus details of Pokémon Go's secrets and Easter Eggs, how to get the new baby Pokémon, a guide to Egg groups, charts, and Egg hatching, details on the Daily Bonuses, finding Ditto, and even which team to join from Team Valor, Mystic, and Instinct.
When will Legendary Pokémon officially appear in Pokémon Go?
It's not uncommon for Legendary Pokémon in the handheld series to be held back to events outside the game - with first generation Pokémon Mew being made available at select retail stores for recent 3DS games - so it wouldn't be a surprise if Pokémon Go follows suit.
Another tease of Legendary Pokémon comes from the game itself, with users who have progressed to level 5 and interacted with a gym find themselves invited to one of three teams - Team Instinct, Team Mystic, or Team Valor - which are shown to be tied to Zapdos, Articuno and Moltres respectively. Could participating in teams play a part in how you unlock these particular Pokémon?
The addition of Pokémon Go's Buddy system also paves the way for players to earn Candy and power up rare creatures without the need to catch any more - perfect for ultra rare Pokémon such as Legendaries. Meanwhile, the eventual arrival of Ditto - which was just as elusive as the Legendaries for sometime - could suggest developer Niantic are finally starting to introduce missing creatures into the game.
In the meantime, an upcoming update will introduce Pokémon trading to help flesh out the gaps in your Pokédex, and our Pokémon Go guide, tips and tricks page to pick up a few pointers you might not know.