Challenging Quests / NPCs

[Dracora]

Last night I did the most challenging quest line I've done in a while. It was a 5 man quest in Valahas or however you spell it. Sort of like the Arena of Blood quests or whatever the name of those are.

I was really happy that it was challenging (especially the guy that had the MS debuff) and I was wondering if anyone else knew of some challenging quests / NPCs? (I'm not talking about Soloing old world boss raids, I've done a few of those already).