Mewtwo

It's from the episode where they show Mewtwo's past. Four other things were being made at the same time as Mewtwo, Amber, a charmander, a bulbasaur, and a squirtle. They could all comunicate telepathically (I got that from Kan). When they were in this dream world (I suspect) or theirs, thay started dissapearing one by one. The three other pokemon went first, then Amber. Only Mewtwo survived.