Instead of a "roll the dice and advance on a board" type of party game, Pirates' Carnival plays more like Othello by way of Mario Party. Before play begins, you select which member of Luffy's Straw Hat crew you'd like to control. Up to four people can play at once, or you can play solo against the computer. Then, you're whisked off to the grid-covered playing field. Players take turns selecting tiles on the grid, most of which trigger mini-games. The winner of the mini-game claims that square, and it turns to that player's color.
By surrounding other players' squares with your own, you flip their tiles to your color, giving you the advantage. Of course, if your opponents manage to surround your territory, they can take the lead back. Play continues until all the tiles have been claimed, and a winner is declared.
It's not quite as easy as that, though, since different types of mini-games and events can sway the outcome of the game. Most of the panels hide a normal, four-player mini-game where all the players compete against each other. More valuable are the Captain Panels, which unveil a card based on one of the many pirate captains in the One Piece universe. These mini-games, which are usually inspired by that captain's role in the anime/manga's storyline, are three-against-one contests, with the player controlling the captain having a distinct advantage. The winner of these events not only claims the Captain Panel, but also a twin panel hidden somewhere else on the board. Earning these two panels can often trigger plenty of tile swapping, so they're a hot commodity.