The Forbidden resembles the Punished.
The Forbidden is a container found only in two locations. The first appears at the top of the Sunken Tower, in the Chorrol Gate realm of Oblivion, and contains Hatreds Heart, Hatreds Soul and Hatreds Soul Arrow.
The other is in the Forbidden Grotto of Paradise, and contains Orthe's Key, required for the main quest, and a random leveled potion. Its appearance is the same as a "the Punished," a large, still beating heart ripped open and hung on hooks.