Which Pokémon game introduced Shadow Pokémon and the Orre region?

Pokémon Colosseum introduced Shadow Pokémon and the Orre region.

Developed by Genius Sonority and released for the Nintendo GameCube, Pokémon Colosseum debuted in Japan on 21 November 2003. Its player character, Wes, is a former member of Team Snagem who can “snag” Shadow Pokémon from opposing trainers.

Shadow Pokémon have had their hearts artificially closed and are used by the villainous organization Cipher. Wes travels through the desert-based Orre region with Rui, a companion who can identify Shadow Pokémon. The story’s cleansing system gives the spin-off a distinctive structure that differs from the standard handheld games.

Pokémon Colosseum is sometimes confused with its 2005 sequel, Pokémon XD: Gale of Darkness. Both games take place in Orre and feature Shadow Pokémon, but Colosseum introduced the setting and the concept. It also supported connections with the Game Boy Advance titles Pokémon Ruby, Sapphire, FireRed, LeafGreen, and Emerald.