Eren was subconsciously using his inherent spell on the human wraith.
Slimy, dark blue smoke made contact with the rotten skin of a wraith. It started melting at a rapid pace and soon turned into a liquid. The wraith's entire skin and muscle on her face and then some more were missing when Eren's left hand in slimy form was done with it.
The wraith couldn't even produce noise anymore because of the liquefaction of the vocal cords along with her face. But that didn't prevent her from struggling with her hands. She tried to scratch Eren with her nails, which she had somehow managed to extend till they reached Eren's body.
Eren was still drinking the weird mixture. But his skin soon turned dark green with crocodile-like scuts over it. This was his body's self-defence mechanism that had kicked in.