I made this account to answer the question about Shadowmere's identity in elder Scrolls. I believe Shadowmere is a horse with vampirism, I have four pieces of evidence to prove this theory. 1- when we first encounter Shadowmere in Skyrim she comes out of a black puddle in front of the Dark Brotherhood's sanctuary in the woods of Falkreath, Shadowmere is een with red eyes, everyone knows one of the first sign of Vampirism are red eyes. 2- Shadowmere' health regeneration, Shadowmere will attack enmies on sight, even if her damage is poor, this can prove useful when the DB is attacking from afar. Shadowmere recovers health much faster than any other human or natural animal follower in the game. Vampires are very strong and hard to kill. 3- with the new DLC in Skyrim, Dawnguard, there are now vampire hunters called the Dawnguard. When you are ridingShadowmere you will experience random attacks from these hunters, even though you are'nt a will alo notice that they re'nt really attacking you, but only Shadowmere. This is a huge piece of evidence proving hadowmere is a vampire, the hunter will also be creaming"VAMPIRE, KILL THE VAMPIRE!" Lastly, the fourth reason Shadowmere is a vampire, Shadowmere is not only in Skyrim, but also Oblvion. No normal horse could ever live that long, nor any normal human. In conclusion, Shadowmere is a vampiric horse.