Rules overview from the official rules:

The game consists of independent consecutive fights. The starting player begins the first fight.

Each fight is contested in one of two elements, either fire or earth, as announced by the starting player of the fight. During each fight, players take alternate turns to play their cards building up power in their combat and support areas. Basically, each turn the players play a character card and possibly some additional cards to at least match the total power of their opponent, who must then in turn match his opponent’s power, and so on. – If a player is unable to do this, he must retreat from the fight.

A fight ends when one of the players retreats. The other player is the winner of the fight and attracts a number of dragons. Both players remove all their cards from their combat and support areas and place them onto their face up discard pile. The retreating player then starts the next fight.

Usually, the game ends when one player runs out of cards and retreats from the last fight. Then the player with dragons on his side is the victor and scores some victory points (crystals). A player wins the game instantly if he has all three dragons on his side and then attracts further dragons.

Description from the publisher.

The world of Blue Moon is in chaos. Its god has abandoned it, and its people are in open war against each other, while the ruling power of three elemental dragons reigns above all! In this original 2-player game designed by Reiner Knizia, each player takes control over one of the Blue Moon peoples - the creative machinations of the Mimix, the fiery Vulca, the lofty Flit, and the clever Hoax - in their quest for dominance. The Blue Moon Legends basic set provides all the material needed to play, including details on the various peoples, a game board, full-color rules, and three plastic dragon figures. Expansion packs contain additional people cards.