So, with Dawnguard i've made a Vampire character, and generally its a lot of fun and I like vampires in TES. Its an interesting blend of various takes on the fanged undead, completely unintended i'm sure, hehe.

However one thing is bothering me and my OCD.

In Skyrim a vampire is not affected by poison, but in Oblivion they were, (edit: and its the same in Morrowind as Oblivion, ust checked) and both types are vulnerable to suffication under water. Why exacly? Game mechanic and abilities they forgot to add? Or do vampires still need to breath, and are some still damaged by toxins? They are undead. Unless the body is functioning, which calls into question the 'dead' part, there is no reason for this. Perhaps simple oversights?

I am tempted to mod in immunity to poison and water breathing both, but I like to roleplay according to the lore. Does anyone remember off hand any references to these things in writing about vampires?

Vampires still have limits to their stamina. Don't forget that.

Well, for one thing (perhaps "pre-Dawnguard" or "pre-Skyrim"), the Volkihar vampires were supposed to live under icy lakes, and are said to reach up through the ice to pull foolish adventurers to their death. So one might assume they don't need to breathe. And there was a clan from Valenwood that could turn into mist (I'm assuming you don't need to breathe if you can turn into mist).

It does make more sense if they don't breath, sleep, eat or are hurt by poison. But like Dargor implied that should probably mean infinite stamina as well and we know they don't have that. I guess it just doesn't make a lot of sense.