Spectator (大観戦, great watch) is an online mode in Super Smash Bros. Brawl available with the game's Nintendo Wi-Fi setup, accessible within the With Anyone menu. Similar to spectator modes in other console games with online connectivity, this mode allows players to remotely view online brawls in action between other players.
Matches you get to view with this mode are totally random, and none of the identities of the players controlling the characters on the spectator's screen are ever displayed. Stages and characters you have yet to unlock will still appear in the matches, and the matches all seem to be two minute timed matches. However, this mode can actually be physically beneficial to the spectating players' own game; they can place in-game coin bets (1-386 coins) on combatants before matches start, and bets on victorious combatants return more coins. The rewards are bigger if the match involves three or four fighters than if it is just a one-on-one brawl, and they often yield more tangible rewards, like stickers. Occasionally, you will be offered a "Bonus Chance" and if you can correctly guess who is going to win, you will earn a bonus reward consisting of several stickers, a trophy, a CD, or a multiple (usually double, but a triple is possible) of the winnings from your bet.
The spectating players' own matches can be allowed by the players themselves to be available for any number of spectators to chance upon and view, by going into the game's Wi-Fi Options submenu and toggling "Allow Spectators" to "Yes".
Spectator Mode actually loads replays of online matches, so allowing spectators will not affect server latency during your matches.
Although Spectator Mode exists, it was removed on June 30th, 2011 but was later returned on July 5, 2011.