WMG: PokéPark Wii

The Pokepark is Heaven for dead Pokemon.
It explains the isolation from other Pokemon worlds, the fact that there are only Pokemon, and of course, Mew is God.

The game takes place in the same timeframe as the Pokemon Mystery Dungeon series.
No humans in sight, vague mentions of them being possibly-extinct in Granite Zone... yeah, wouldn't surprise me. Given Darkrai's gentle demeanor in the Haunted Mansion, it's hopefully after the Explorers games.
  • Hey hey, Corphish's appearance kind of confirms this one!
  • Made more likely in the sequel, with the presence of Wish Bells, which function like Time Gears. Not to mention Darkrai, whose angst in this game may be either a result of or a prelude to MD 2.

Rotom is the one Charon knew.
You find it in an abandoned lab, in a mansion. Ok so the Old Chateau is way back in Sinnoh, but the abandoned lab? Poor Rotom hasn't seen its scientist friend since all the humans went away so it's waiting for him to come back.