Under Your Skin is a group instanced mission first introduced at Halloween 2010. It is expected that it will return every year at Halloween.
It is given by Rhaeda Evel in Plane of Knowledge by the main bank. It is necessary to do the Terror of Illis Taberish mission to request Under Your Skin. The reward is a undead rabbit pet for your house.
Tell Rhaeda Evel "ready" to zone into instance. You can leave mission any time by clicking on the door next to where you zone in and you will return to Plane of Knowledge. Tell her "ready" again to return.
You must go to the north west most room in the zone. You can either kill your way there or run and feign death (if your class allows).
Once there, hail the Skinwalker. He will despawn and be replaced by three identical "Revealed Skinwalker". The task says you must identify and kill the real one. If you kill a false one, two Revealed Skinwalker will spawn at the place you killed it.
Either the real one is decided at random, or it is the one standing closest to the non-attack-able werewolf on the stage.
Kill the real one and the other mobs will despawn. Elder Longshadow will spawn. Hail him to complete the mission.