Abomination

Abominations are the result of alien experiments on abducted humans. They are found only aboard Mothership Zeta. The name "abomination" is derived from what an escaped abductee calls them after discovering them, as recorded in alien captive recorded log 19.

Biology
From what can be ascertained through various audiologs, abominations are captured human male or female test subjects hybridized with alien DNA, intended to be used by the aliens as biological weapons. The transformation process (of which the details are unknown) turns the subjects into feral, menacing creatures - hostile to anything that is not one of them (including the aliens that created them), and they lose all discernible sexual characteristics, leaving them with an androgynous appearance. It is unknown if there are more of them on the ship after finishing the Mothership Zeta add-on. Their known creation history and asexual appearance seems very similar to super mutants, while their hostile behavior and lack of self-preservation mirrors that of the feral ghouls of the Capital Wasteland.

Combat
When spotting a target, an abomination will point and wail loudly (possibly to rally others of its kind), then move quickly into melee range to attack with its long arms. Their attack methods are very feral ghoul-like. They are a fairly standard opponent and are easily blasted to bits by alien weapons.

Loot
When they are killed their body can contain normal alien items like alien power modules or alien epoxy but sometimes human items can be found like packs of cigarettes, pre-War money, harmonicas, human flesh, baseball gloves, pre-War books, bobby pins, etc.

Appearances
Abominations appear in the Mothership Zeta add-on for Fallout 3.

Behind the scenes
The way that the abominations point and screech when spotting the player may be a reference to the 1978 movie "Invasion of the Body Snatchers", in which the alien "pod-people" do the same thing.