Hey all, I did use the search option on the forum with keywords: Invisible, Attack while Invisible, and Nibelung and nothing came up, if it's a repost i'll delete thread asap.
First off I only tested this with mage, but I suppose it could work with night elf casters aswell.
For this trick you need the staff Nibelung which drops off Lady Deathwhisper in Icecrown Citadel 25 man,
now for the exploit: If you get a val'kyr spawn from Nibelung (you can get up to 3 at a time) and then cast Invisibility (as a mage) the val'kyr will still attack the target.
This is not working as intended (for mage atleast) because up and till now the only pets I ever saw attacking some one while invisible are these Guardian val'kyr.
Summarized:
1. Get Nibelung
2. Get adds to spawn
3. cast invisibility
4. watch adds still attack(you can still see them)
5. ???
6. profit
PS: these add will keep you in combat so you can't just invis and go eat while adds are attacking things.