Spooncraft

One of the only truly hard fights in MGT (especially in heroic mode) would have to be the 3rd boss, Priestess Delrissa. The fight itself is pretty much untankable and plays more like a really imbalanced 5 vs 5 arena match than anything else. Rogues are taken out of stealth as soon as the mobs are engaged and this is intended.

This is an intended part of the encounter, rogues should be removed from stealth when the NPCs are engaged. (src)

I kind of agree that this is stupid.