From Wikipedia
Bomberman Online (not to be confused with Online Bomberman) is a multiplayer game for the Dreamcast. It adds new ideas to the original formula with online play, new playing fields, and other extras. Bomberman Online's servers were shut down in 2003. Unfortunately the game does not allow "direct dial" play unlike its cousin (Saturn Bomberman), which means muliplayer is now restricted to offline only.
Multiplayer Modes
Survival Rule
This is the original Bomberman battle mode. The winner is the last one standing. This is the mode you'll be playing when you are fighting against the Electric Dragons. The boss of this stadium is Thunder Bomber.
Hyper Bomber Rule
A new mode to the Bomberman series. To win, collect 3 target panel power-ups, and touch the center place. A huge explosion will then kill everyone but you. For each target panel you get, a skull will come and circle around you, so you can keep track of how many target panels you have. Getting killed loses all of your target panels. This is the mode you'll be playing when you are fighting against the Red Phoenix. The bosses of this stadium is the Bomber Brothers.
Submarine Rule
This game is almost identical to Battleship, except that it is realtime. You place a bomb down with a timer on it, and once it gets to one, it goes over to the adjacent spot on the other side. This is the mode you'll be playing when you are fighting against the Princess Mariners. The boss of this stadium is Bomber Mermaid.
Panel Paint Rule
The object of this mode is to color as many squares as you can your color. You can do this by blowing up a bomb, and every square that the explosion touches, turns into your color. If you die, all the squares your color turn into the neutral brown square. This is the mode you'll be playing when you are fighting against the Iron Bulldozers. The boss of this stadium is Bomber Gun Rock.
Ring Match Rule
In ring match mode, you try to kill the opponents to gain points while not dying yourself. As soon as you die, you are regenerated back onto the playing field. This is the mode you'll be playing when you are fighting against the Storm Giants. The boss of this stadium is Aladdin Bomber.