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. In addition to this, upon his defeat, the Undead King Set would have been made available to the player, either through Domhnall of Zena or some other means.
Work from the Dark Souls community has revealed that, when Jar-Eel was removed from the game, the developers had implemented a slightly modified version of the moveset of Old King Allant from Demon's Souls. 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. Jar-Eel wields both a unique Curved Greatsword, which is unavailable to the player, and a Dark Hand, however, in addition to sharing the voice of Old King Allant from Demon's Souls, his attacks with the Dark Hand could also steal soul levels.
The video below is a demonstration of one such community member's efforts:
- ↑ Dialogue with Ingward which was removed from the game
- ↑ 5 Things You DEFINITELY Didn't Know About Dark Souls! - VaatiVidya