The Official Pokémon website just officially revealed a new Mythical Pokémon, Meltan!
A day before Chikorita Community Day, it's 3D models and sprite images was dumped from Pokémon GO network traffic.
The dumped 2D sprites and GIFs of the animation as below:
Model and animation dump credit: https://twitter.com/Chrales
Right after Chikorita Community Day, Ditto started masquerading as Meltan appeared in the wild in Pokémon GO.
Here are some screenshots of the outbreak on the day itself.
[Technical info: The developers temporary replaced the unreleased Kecleon with Meltan's models, animations and cries]
Here are some official screenshots:
Various pages and sources:
Meltan Reveal Page
Prof Willow and Oak's Discussion Video (Episode 1)
Pokemon.com with Tweets relating to Meltan