What is the difference between Pokémon Diamond, Pearl and Platinum?

Pokémon Platinum, released in Japan on September 13, 2008 and in North America on March 22, 2009, is the single enhanced version of Diamond and Pearl, with Giratina on the box. The story is reworked around it: at the Spear Pillar climax, Cyrus summons both Dialga and Palkia, and Giratina drags him into the Distortion World, a full new area the player explores before the credits rather than after them.

The Pokédex is the deepest change. Diamond and Pearl's Sinnoh Pokédex held 151 Pokémon, of which 150 had to be seen; Platinum expands it to 210, pulling in the cross-generation evolutions the originals had locked away until the post-game, and asks you to see all 210, Manaphy included, which can now be done by reading a book in the Pokémon Mansion. The expansion also fixed the pair's famous Fire-type drought, which had left Chimchar and Ponyta as the only Fire lines in the regional dex.

Around the edges, Platinum is a long list of answers. The lone Battle Tower of Diamond and Pearl's Battle Park becomes a five-facility Battle Frontier. The GTS building grows into the Global Terminal. Surfing is fast again. Twinleaf Town wears snow, the heroes wear scarves, and two new characters, the detective Looker and the Galactic commander Charon, thread through the plot.

Platinum also introduced new formes that only it can hold: Giratina's Origin Forme, Shaymin's Sky Forme and five appliance forms for Rotom, unlocked by the event Secret Key. Traded back to Diamond or Pearl, those formes revert, which makes Platinum less a replacement for the pair than the version of Sinnoh that contains them.