Hmm, Giratina. If Dialga and Palkia are the masters of Time and Space, Giratina is the master of anti-matter and chaos. It rules the Distortion or Reverse World, a world where the laws of physics do not apply (waterfalls go up and trees grow down). Through the Distortion World, Giratina could appear anywhere it likes. Legend has it was banished by Arceus at the beginning for its violence. The Reverse World in the anime acts like dumping ground for abnormal pollution. If there is imbalance in time and space, the Reverse World absorbs to correct the balance. And apparently, the Distortion World in the Adventures manga is also where spirits of the deceased may end up. It's possibly related to the Ghost World or the World of Spirits, a place where malicious Ghost Pokémon (or people) may try to lure unsuspecting trainers to.