After Niantic released Legendary Pokémon during the Pokémon GO fest. They have tried very hard to keep new Legendaries up after old ones reach their end dates.
Ho-oh’s end date is on the 12th of December which must mean Niantic already has another Legendary Pokémon in mind to finish off December, but which one is it?
As of right now, there are only 2 Legendary Pokémon in the game that has yet to be released into the game. It is possible Niantic will release Mewtwo and have the EX raid feature complete around the 12th. Releasing Mewtwo around the same time it was seen within the teaser trailer for the game.
However, the next Legendary could still be Mew or Celebi. As of right now, Celebi seems to be a forgotten Legendary Pokémon, so it’s doubtful we will see that one anytime soon. More trainers are talking about Mew than Celebi putting Mew higher up on the to-do list for Niantic.
Generation 3 is theorized to be coming out very soon. Niantic mentioned they would try and get generation 3 officially released around December. Which would bring new Legendary Pokémon. Though, generation 3 will probably be released before Niantic adds those new Legendary Pokémon to the game.
This means if we don’t see the rest of the next generation Pokémon before the 13th of December. We won’t see the next Legendary Pokémon being of the new generation. So this makes Mew or Celebi most likely to be seen next.
While Mew is more sought for than Celebi. It wouldn’t make a whole lot of sense for Niantic to release a time-based Pokémon around a holiday like Christmas. It’s not very strong and not a well known Legendary Pokémon. It would make more sense for Niantic to release a Legendary Pokémon that several trainers know, which of the 2 unreleased, is Mew.
It is also Possible Niantic will do a two week period of all released Legendary Pokémon as raid bosses. This would give trainers who missed any another chance of catching the Legendary that might have missed. It would also randomise which Legendary trainers will see out of a 5 tier egg. With only 1 Legendary popping out of an egg. It kind of defeats the purpose of there being an egg, to begin with.