Aberrations are from the Hell Pit army list:

"Aberrations are beyond classification, the aborted experiments of crazed Moulders whose ambitions outweigh their skills. Invariably driven mad by their fate, Aberrations will go to every length they can to ensure that their miserable lives are drawn to a close as quickly as possible. Aberrations often plead for death as they throw themselves upon the enemy's blades."

Wielding a nightmarish assortment of snapping mouths and mutated limbs, these unbreakable monstrosities are roughly equivalent to a chaos spawn, although the fixed movement value makes them slightly more reliable.

Nothing terribly imaginative in this conversion. Just a chaos spawn with a rat head, spikes, and an extra arm with a sword. I didn't think the original chaos spawn feet made it appear as much like a rat ogre as it should, so I used the plastic rat ogre legs to lengthen them some. This turned out well, and even gave it a more top-heavy skinny-waisted appearance like the rat ogres.