The Dimensional Horror are beings of immense power and dread.
They resemble annelids but only being black and gigantic. The Horror have appendages although they are useless in our dimension. However it use its limbs so it can breach the area surrounding it in order to protect itself. They have one large gaping mouth which they use to discharge a powerful beam of unknown energy.
Known to inhabit areas where the boundaries between our dimension and its dimension is at it weakest, these beings can be commonly found around black holes. Despite being able to breach our dimension the Horror is eternally stuck between dimensions, so no-one has been able to fully see a Dimensional Horror in its entirety.
This may have been the case but one did fully breach our dimension, although briefly. Only known as the Worm by the races it selects, this particular Horror has intelligence unlike the others. Races selected by the Worm had been chosen since before they had crawled out of primordial ooze. The Worm, when it was inhabiting normal space, would call out to this particular race, influencing their very existence. It would have a major impact on the race's development historically and evolutionary. At one point in time this race rejected the Worm and its "love" and called upon a unknown benevolent race to banish it. It eventually returns, barely breaching the dimensional barrier, and starts calling out to the same race again. If the race chooses to listen and accept its love wholeheartedly, they will transform back to their primordial selves and begin building a device to allow the Worm to reenter our space.