I'm not quite sure but my shadowfiend seems extremely squishy since 4.3... :S
It happened both in DS 25 normal and LFR that I summon the darned thing and regular aoe damage just kills it off right away. I'm pretty sure that it is supposed to have some sort of built-in aoe resistance like most other pets do (and it usually lives just fine in aoe environments) but these two raids it has been dying pretty much right away.
Some priests from the guild were saying they have experienced the same thing... anybody else that has noticed anything similar?
It is quite infuriating to get 5% mana back from a 5 minute cooldown because it dies straight off in most fights... :S