No matter how infinite, I don't think a world closely resembling Pokemon is likely to exist naturally. In that case, it is not a matter of environment, but technology. Pokemon are shown to be teleported across the world through PCs, which is not possible even with quantum entanglement unless they can be created instantaneously using some sort of data (which means they are not naturally occuring lifeforms). Pokemon like the creation trio can also be ruled out easily, so can anything related to Psychic-types.
If it's a world like Pokemon you seek, something like Google Glass + AR generated Pokemon/battlefields shared between multiple people anyone? I honestly think that could happen in the near future.
If you disregard things like psychic and ghost types, the ability to communicate with humans, legendaries controlling nature, flashy attacks and the technology of the Pokemon world (none of which, besides communication, can exist naturally), it's pretty much Earth TBH.