Undead King Jar-Eel

 is a boss which was removed from the final release of Dark Souls.

General Information
It is unknown where Undead King Jar-Eel was supposed to be located in the game, however, it is possible that he was going to be located in the New Londo Ruins, and had to be defeated in order for Ingward to present the player with the Key to the Seal.

Work from the Dark Souls community has revealed that, when Jar-Eel was removed from the game, the developers had made parts of his moveset. As a result, through modifying the game files through third-party programs, it is possible for the player to fight Jar-Eel instead of a boss encountered normally.

The video below is a demonstration of one such community member's efforts: