No bets are allowed in round 5. This is a nice feature, as players must judge whether or not to place a valuable bet early in the game then try and keep that creature alive. Only 1 player can bet on a creature in any given round, which is another nice feature. By betting on a creature, you may become it's 'backer'. A backer of a creature is the player with the highest value of bets on that creature.
Backers can invoke a creatures special ability.
Players can also make a secret bet in round 1. Secret bets are worth 5, and are kept hidden by placing a token on top of a face down strength card of the creature being backed. Secret bets can be voluntarily revealed later in the game, usually if a player wants to take over the role of backer of a creature. Playing a card is as simple as it sounds. Players are trying to keep their creatures going and eliminate other players creatures at the same time.