Board Thread:Questions and Answers/@comment-6011882-20130308145601/@comment-5706972-20130308161505

The Battling page makes mention of the element bonus:
 * Account Element
 * When players first create a game account, they are asked to select one of the three elements. The player automatically receives a 5% stat boost for using cards of that element in battle.
 * Elemental Effects
 * When in battle, element matches somewhat affect attack and defense ratings. Fire cards have reduced attack against water cards, water cards have reduced attack against forest cards, and forest cards have reduced attack on fire cards. Likewise, fire cards have increased attack against forest cards, and so on. Only one element effect may take place at a time.
 * Elemental effects are determined by the element of the players involved in battle. Fire players attacking with fire cards against water players with water cards will result in a fire versus water match up, regardless of whether other elements are present in either deck.