I was trying my hand at some leading taming, after following a video guide here:
I saw they would cast invis to break Cu Sidhe aggro. I noticed after I angered a Cu Sidhe here, I would go invis, but then after coming out, he immediately attacked again. This caused me to find out that after death, they still hold that aggro. They will keep attacking until tamed or dead, even leaving the dungeon and coming back.
In one attempt to get my body back, I used Ethereal Voyage, and the Cu Sidhe immediately started attacking me while in the Voyage. Only named monsters are supposed to be able to see through it: http://www.uoguide.com/Ethereal_Voyage
It seems you are even supposed to be able to anger it while in EV and it still won't attack according to this old post: https://stratics.com/threads/ethereal-voyage.153212/
In one attempt to get my body back, I used Ethereal Voyage, and the Cu Sidhe immediately started attacking me while in the Voyage. Only named monsters are supposed to be able to see through it: http://www.uoguide.com/Ethereal_Voyage
It seems you are even supposed to be able to anger it while in EV and it still won't attack according to this old post: https://stratics.com/threads/ethereal-voyage.153212/