Abomination

 are the result of alien experiments on abducted humans. They are found on the board of Mothership Zeta. They appear to be a hybrid of a human and an alien, and they are hostile to anything that is not one of them, including aliens.

Loot
When they are killed their body can contain normal alien items like alien power module or alien epoxy but sometimes human items can be found like pre-war money or harmonica

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