Bridge of Eldin is a stage in the Wii video game Super Smash Bros. Brawl. The stage is probably the flattest stage in the game, and for a while the stage where barely any thing goes on - that is until the King Bulbin from Twilight Princess enters the fray attacking everyone and dropping bombs on the bridge, thus destroying it. Later on, the bridge will be repaired, though it can be conclusive that the malevolent creature will return and perform the same attack once again.
Your characters will have to jump over the gaps once part of the bridge have been destroyed, or he or she will die.
The Bridge of Eldin is a location found in The Legend of Zelda: Twilight Princess. It's located in the Eldin Province area of Hyrule and is a way to get across Lake Hylia easily. In the game, this is where the incredible battle against King Bulblin and Lord Bulbo takes place (twice!), and both of these creatures will appear on the stage in Brawl and destroy the bridge. Eventually the segments will be returned though a dark world portal type thing, sort of referencing a part in the game where Link and Midna would recreate a bridge in a similar way. Various fields, castles and villages from the series can be seen in the background.
The King Bulblin was featured as a boss twice in The Legend of Zelda: Twilight Princess - both times appearing on the Eldin Bridge. Some may not consider him a boss, though it's unarguable that it was one of the most memorable battles in the game! You'll fight him, or at least a similar beast, right outside of Hyrule Castle and you'll once more have to fight him, though once you're finished he'll pledge allegiance to the side with the best chances, that being Link's after he witnesses his strength.
In the background of this stage you can see Hyrule Castle. This location has been featured in a variety of games, though this particular one was featured in The Legend of Zelda: Twilight Princess. In this game it is the final dungeon and is where you'll fight two of four final bosses (Puppet Zelda and Beast Ganon). In the end of the game, the entire castle collapses, though both Link, Zelda, and even Midna are safe from harm's way.