Shadow Pokemon are normal Pokemon who have had their heart sealed away and only care about fighting. Shadow Pokemon have had the door to their heart sealed.
The criminals responsible for this act is known to Orre as the organization Cipher. In order to make their deeds, they force upon merciless fighting and pinned as utilities instead of being the treat with the kindness and respect the creatures, known to all as Pokemon, deserve.
In both Pokemon Colosseum and Pokemon XD: Gale of Darkness, the Player must capture these Pokemon, and open their hearts, returning them to their original state. In Colosseum, shadow pokemon can only be cured through , who would bring them back to a time before their hearts were sealed, purifying them.
Pokemon XD introduces the purification machine, which involves synchronizing pokemon based on their type to purify a shadow pokemon.
Pokkén Tournament features the playable fighter Shadow Mewtwo. In this game the Shadow Synergy Stone took control of and merged with Mewtwo. Under the influence of the Shadow Synergy Stone, Shadow Mewtwo traveled around Ferrum, draining Gaia power from the normal Synergy Stones and continually increasing its own power.