This is random, but one thing that really bothered me was when Leliana slit the throat of Felix... Here's why:
I read somewhere that Alexius used necromancy to re-animate his son, who is clearly some sort of zombie (based on Dorian's shocked reaction to seeing him). Why would a re-animated corpse die from having its throat slit? And couldn't Alexius just re-re-animate him? If Tevinter magisters can use blood magic/necromancy, why would he throw a hissy fit and attack the Inquisitor? :\
I don't think he was an actual Zombie. He most likely did something to his son when his son was about to die that kept him from dying.
I have a theory:
Zombies in Thedas are basically corpses possesed by demons. But with Justice we saw that any spirit can control a corpse.
So Necromancy is basically bringing a spirit, in most cases demons, from the fade into a corpse.
Now it is said that the souls of the dead travel through the fade to the makers side and get lost and have to wander the fade forever, if they stray from the maker in their mortal life.
Now what i am thinking is that Alexius used Necromancy to get his son's soul, while it was traveling through the fade towards the maker and bind it to his own corpse. It would still be the sons soul in his sons body, but that body would be a corpse and not a living body. It would explain why Alexius sees his son in that thing and why his "son" appeared to be rotting in the demo.
As to why he not just re - reanimates his son. As we see when we fought undead in DA:O the possession of a demon on a corpse can still be severed when the corpse takes physical damage. Why he not re - reanimates him immediatly i don't know, but my guess would be that it takes time to prepare to really force a spirit or soul into a corpse. The reason why necromancy as an ability in the game would be faster would be that they are bringing demons into the corpses, which are willing to possess the corpse and don't have to forced, just enabled. He probably had enough time to prepare when his son innitialy died, but not now when it happened out of the blue he had not.