Update of klouds adventures in skyrim:
(Btw, summer, I realize thats a standard werewolf rumor. The fact that they said it to a Khajit is what makes it dumb.)
Shadowmere is dead, and I have no idea how he died. I just explored a ruin, and left him outside like I always do (because I thought he was immortal), I came outside and saw the following things:
The corpse of two giants.
The corpse of three mammoths
An Expert Necromancer, and two ash piles of unidentifiable descent.
A blood dragon.
In the middle of all this was Shadowmere, with 108 steel arrows on his body, and he was dead.
How did the horse that charged straight at a blood dragon and did not even take a hit on his health bar, as well as regenerating fast enough to take a whole banditry(?) of bandits while I fired at them with my bow (and yes, hitting the horse too. But it didn't matter, cause he didn't ever take a hit to his health bar) fall to this ridiculous combo? I have no idea.
Next to his body I found a live snow bear.
The only way I've experienced that Shadowmere can die is from falling due to it one hit KO'ing him thereby not giving him time to heal. He's not immortal, he just heals at a blinding speed. Theoretically if you pummel him with huge damage in a very short time frame he can be killed. Giants can inflict this much damage, and so can mammoths. It doesn't seem improbable most certainly.
Do you have a recent save that you can revert to?
Update since I got this on PS3:
Dark Elf currently level 42.
Light armor, duel wields ebony war axes, also skilled in archery.
I have seven Daedric artifacts and one dragon mask.
I'm just before World Eater's Eyrie in the main quest.
I finished the Companions questline.
I finished the Dark Brotherhood questline.
I'm half way through the Thieves Guild.
I joined the College of Winterhold just for the room before I bought the house in Markarth.
I use epic Nightingale armor solely because it looks sooo much better than glass armor. (You have to drink Blacksmith potions to get it to Epic)
Lydia died. My follower is Aela.
I am one badass muthafuzzer.