It came from my mind!
Seriously though, mostly it comes direct from the games. There are ways to extract the data like Pokemon and moves from the game's code. People smarter than me do that and it's used by all the Pokemon sites.
All the articles and paragraphs of text are written by me. We do have some people contributing various things (especially the upcoming Pokedexes) and pointing out errors, which I am very grateful for.
