Monstrous beings taken a step beyond, beings so hideous that viewing them drives people insane or their very existence is affront to laws of nature. Or just some exceptionally ugly monsters that do not resemble much anything real.
The first video game about Abominations was released in 1987.
In some instances player never actually gets to seem the actual abomination, but gets to feel the effect of their reality bending existence/powers.
* The Thing
* Shoggoth and others from Cthulhu Mythos