So I was out exploring the world on horseback with shadowmere, and I decided to park him on the side of the road to pick something up. As I left and picked up the item I saw, I turned around to see him randomly attacking and eventually killing a couple of deers on the side of the road. Now, according to what I've read, deer are peaceful creatures and DON'T attack unless provoked, so shadowmere must've instigated this. Has anyone who has shadowmere had this happened to them? Its not a problem for me, it's just kinda strange that he would suddenly develop homicidal tendencies and take it out on nature.

it's not just shadowmere, all horses do that, probably skyrim's horses are all badass

You do remember where you got Shadowmere from?

Now, thinking about that ask the question again and see if you can't answer it.

It's not surprising to me. However, I think it might have been more of a glitch than anything else.

Dectect Life spell shows Deer and other wildlife as enemies (Red Aura) Maybe this tag is what is setting shadowmere off.

I do hate that horse - because it just goes around killing everything and is a bit too silly for my taste. I really wish horses wouldn't act like this in skyrim.

I lol'd hard at this. My shadowmere is terrible, it even came up and killed a lone NPC while I was talking to him -.- then proceeded to shoot up into the sky and I never saw it again so I had to reload my game.

Nevermind OP, I'm sure a prancing Unicorn mod for the pacifists among us will be released soon.

_{Shadowmere is the boss. Attacks anything that moves & climbs hills like a [censored]ing mountain goat. I got ambushed by hagravens & he pissed off to kill a sheep. lol}

The very first time i got a horse in Skyrim i thought i'd be careful in protecting him, my first encounter while on a horse was two frost trolls. They had not seen me so i stopped my horse a fair distance away so that i could go on ahead and deal with them without the risk of losing my horse. Yet as i start charging down the hill towards the two trolls i suddenly see my horse gallop past me and charge both trolls full on. Needless to say he died and i had to walk back to town.

Very aggressive horses indeed.

Even the Character mentioned that Shadowmere is one of "us".

Thus stating he's a pretty B.A.M.F. horse.

All horses are like this I got frost and when I fast travel and there enemies near by he go right for them it's like all horses in the game have a death wish or something.

Shadowmere is also a Aspect of Sithis/Nightmare. So it makes sense for him to be a homicidal psychopath with a craving for fresh blood/flesh.

Yeah, so I killed my Shadowmere. Horse needs to have some common sense and not decide his masters battles.

Shadowmere is glitched that way, same as all the horses in Skyrim.

But for Shadowmere it actually fits imho.
She basically is a badass homicidal biatch. Atsrid says about the horse that it is: "One of us". Which basically covers it.

[edit]
Shadowmere will respawn after 15-20 days though. Have fun.