Any lore (fan or official) on death hounds? I presume they are undead/constructed somehow, bearing in mind their appearance? Or are they just fugly creatures?

<sup>Oh yes, I've been waiting for a quality question to arise in these parts.

But sadly, I have no answer sinceI am wondering about this as well. Closest thing we had to Death Hounds were Hellhounds from Arena.</sup>
"These canines are actually from the nether planes, usually summoned by some powerful being to perform a service. They attack with their powerful jaws, or with a fire breath that burns their intended victims. They are resistant to fire-based spells."-Arena.

They're either related to Hellhounds, or they're some sort of constructed animunculi like Gargoyles. Serana does mention her mother has a fascination with such constructs.

They were probably dogs in life, and when they died a necromancer summoned them again.

I assumed a construct as well, because even dead, those dogs are ugly as [censored]. Hellhound, though...

What? They're adorable!

They remind me of Shivering Isles http://www.uesp.net/wiki/File:SI-creature-Skinned_Hound.jpg.