Hoard

Hoard were extra-planar collective entities in the I.C.E. Age, resembling seas or humanoid mud forms, while actually being colonies of mutually self-aware single celled organisms. Hoard were able to sense all of the other hoard colonies across planes of existence, and when threatened would all know who and where to go if possible for retribution. In the humanoid form they were twelve feet tall, coincidentally the same height as the avatars of deities, and when fighting could split themselves in half to increase their numbers. The colony would only die if its parts were too dispersed.

Hoard had a strange ability to sense dimensional warps they could travel through, and would wander across many planes of existence with no apparent homeworld. These had sorcerous and mentalist powers such as pain infliction, and physical contact with them would cause a mind jolt kind of effect. It was impossible to summon hoard, and they were immune to slashing and puncturing. However, those of The Broken Lands may have been artificial, owing to the work of Uthex Kathiasas. Twelve feet is the height of the crystal dome as well as the statue of Morgu (Marlu) in the Dark Shrine.

Behind The Scenes

The grey mud sea on the jagged plain of The Broken Lands is implicitly made up of Hoard colonies. These were "other standard" extra-planar entities known to exist on many planes, similar to the source material behind other creatures such as the magru, dark vorteces, and crystyls. These all tended to have unknown homeworlds, the inability to be summoned or only accidentally, and being known for finding their way onto other planes of existence. Hoard, crystyls, and traag were only implicitly present in the game, whereas Uthex gave the others different names mostly in the dead language Iruaric.

The following is what hoard look like on the jagged plain. There seems to be no way to interact with them, and telepathy does not work in The Broken Lands. It is impossible to "reach out with your senses" outside the workshop, because "something seems to be blocking them." When you are too close to the crystal dome transportation magic like Spirit Guide (130) stops working. These factors interfere with the possibility of communicating with the hoard, and perhaps even keep them bound to this plane of existence, which may explain why they have become a whole sea of mud.

[The Broken Lands, Jagged Plain]
A huge sea of boiling mud stretches out to the south and east.  Steam rises off the churning mass, choking the air with a dense, malodorous fog.
Obvious paths: north, southwest, west, northwest

>look mud
The mud is predominantly a grey-brown color, but there are patches of green and orange mud here and there.  A thick, grey steam rises off the surface of the mud.

If the hoard correspond to something from "The Dream-Quest of Unknown Kadath", it might be when the quest seeker "sought a forest pool and cleansed himself of the mud of nether earth." The forest in this context would be the "crystal forest" of crystyls to their north, with the two seemingly avoiding each other. It is interesting because Iruaric is actually a telepathic language.