Sinnoh is the region in which Pokémon Diamond and Pearl are set. It is a widely varied area, with a large chain of mountains dividing the region in half. The most notable of these mountains is Mt. Coronet, the peak of which is the legendary Spear Pillar.

In Super Smash Bros. Brawl

The Pokémon stage Spear Pillar is located in Sinnoh. Spear Pillar is supposedly the area the Sinnoh region(if not the entire Pokemon Universe) was created and is thus very important in game. The player character of Diamond or Pearl battles the leader of the evil Team Galatic here and capture either Dialga or Palkia. Much later in the game, it is possible through the use a special item to battle the strongest and rarest Pokémon of all, Arceus. Arceus does not appear in Brawl, as it wasn't officially open to public at the time, although Dialga and Palkia both appear as background characters on Spear Pillar.

Sinnoh region may also be home to the stage Pokémon Stadium 2, however, this stage could be practically anywhere, considering that Pokémon battling is common to most of the Pokémon world.