The expansion costs $9.99 to purchase and download but when installed with the original game adds the ability for the player to team up with up to seven more players to face down the single player storyline. There are a couple of differences between single and multiplayer (monsters get harder the more players are in the game and there are infinite lives for the players in multiplayer mode) but besides that it's basically the same game. The expansion is available for both the PC and Mac versions.
Download the Kivi's Underworld demo for PC and Mac at Big Download
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