If someone finds a bulbasaur, they can post the first post of a wild encounter of a bulbasaur. The next one sends a picture of an ivysaur encounter, etcetera. Must be in international Pokédex order. (Pokemon go Pokédex lists Pokemon according to the international dex)
Pictures can be in your library, as long as it is an encounter picture with that Pokemon.
6 hour rule applies here
Explanation: if you posted a Pokemon, and no one has replied for the next one, you can send that one.