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. The tension is really noticable, and makes for some terrific game play. Also, if a backer plays a strength card on their backed creature, they can invoke that creature's ability.
Spectators can be useful, or a hinderance, and is a nice feature to add to the game.
The Referee cards can be played instead of taking a normal turn. The 'Head Referee' can be played above a creature and will force all secret bets made on that creature to be revealed. Normal 'Referee' cards allow any card to be taken back into that players hand. Finally, at the end of the round 5 there will be only 3 creatures left in the Arena. All remaining secret bets are revealed and totalled with other bets.