Royal Rumble

In a normal Battle Royale, all the participants (usually 15-30) start in the ring together and duke it out until only one is left in the ring.  This leads to a giant clusterfuck, since there's too many things going on at once for anyone to follow the action.

So, to make battle royales more TV-friendly, the concept of the Royal Rumble was born.  All 30 participants draw lots to determine their seed.  The #1 and #2 seeds start already in the ring.  Every two minutes (90 seconds some years), the person with the next seed joins the fight.  This drastically improves the flow of the match, as there usually aren't more than six or seven guys in the ring at the same time. It also lets fresh wrestlers keep the match moving, preventing everyone from blowing up and bogging the match down. The only way to get eliminated, as with most battle royales, is to be thrown over the top rope and have your feet hit the floor.

This unique style allows the spotlight to be cast on many different roles.  Traditionally:
 

• The #1 (or #2) seed are the "marathon" spots--by lasting upwards of 30-40 minutes into the Rumble, they show that they're great competitors with incredible stamina, and the fans get behind them to see if they can last the whole way through.  Shawn Michaels actually won the Royal Rumble in 1995 as the #1 seed.
• The #30 seed is usually hyped as the "heavy favorite" since they'll be fresh when everyone else is worn out.  It's become a Sword of Damocles, however, as no #30 seed has ever won the Rumble.
• There's usually a monster big guy who comes in when there's a shitload of wrestlers in the ring and clears them all out.  This was done most effectively with Diesel.
• There's always one "oldtimer," a former star who puts in a brief appearance.  Honky Tonk Man, Bob Backlund, and Jerry Lawler have all filled this role.
• There's usually another "surprise" wrestler who isn't on the WWF roster.  Most recently, Haku made his WWF debut in the 2001 Rumble immediately after jumping ship from WCW.