Typically I have no problem downing Elites, some tougher than others, but I have to say there was this one mob in particular during my vision-quest in the Voss Temple of Healing that just did an insane amount of damage, dropping my well-geard companion in no time, had a charge leap and constantly AoE stunned me.
After about 6 attempts, the closest I got it down was like 2% and I was 2 levels above said creature. Considering I had downed other Elites of the same creature during the mission, this one seemed waaaaaay over-tuned, either that or was mislabled and meant to be a Champion mob. I should have compared Health Points with other elites in that mission to be sure. This one had around 26k HP, which seems more than usual but not enough to be a full-fledged boss.
Ability delays during crucial moments didn't help, either.