Yu-Gi-Oh! Capsule Monsters, FOX (USA)
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Apparently set somewhere within season 5 of Yu-Gi-Oh!. Yugi and his friends were playing a new board game called "Capsule Monsters." And then Joey won a trip for four to India, and took Yugi, Tea, and Tristan with him. But their plane went down on some island or whatever, where they met an archaeologist named Dr. Alex Brisbane, who said he had been working with Yugi's grandpa, who had disappeared. So they all went to look for him in the pyramid he'd been exploring, and the kids ended up transported to a world that was just like the Capsule Monsters board game.
And, well, they'd all acquire various monsters there to fight for them, and they'd eventually face a series of challenges before they could return to their own world. And then there was this whole thing with the spirit of Alexander the Great (or actually two spirits, his good side and his evil side). And Yugi and his friends would have to battle him, after they'd escaped the capsule monster world, because he wanted to claim a power that would allow him to control the world.
And that's pretty much all I can say. The show is only 12 episodes long, and I think it was made originally for the U.S. market (and never aired in Japan). And, um... it was okay, I guess, but it doesn't really stand on its own, it's not worth watching unless you're a fan of the main series. And even then, it's not as good. It's not so much that there's anything wrong with it, it's just kind of pointless.