If you use levitate in the arena, seawatch coast, tou will have a permanent invisibility. but there's a catch, if you go outside the arena they can see you or if they step outside the arena (past the enforcers by the antrance and past the small bump) they can see you.
This goes for the WHOLE arena not just in the middle

Also, if you only use dps and no skills or spells you can kill people with ease because they can't target you and you can also send your pet on people
[Edit] I think it works in any dungeon.