The transmogrify lasts 6 minutes and makes you appear to be one of the Blood-Drained (non-KoS to all the mobs in the area). Hail Lillithiara and offer your blood to her. When she bites you the poison makes her as killable as a normal mob. You will lose the illusion when you attack her, and after she is dead you will be unable to reuse the poison to gain the illusion's protection, so you will have to Recall or fight your way out (and maybe die and revive) to get out of there.