Arvak

Arvak is an undead horse that appears in. The Dragonborn can obtain Arvak as a mount after finding his skull in the Soul Cairn.Then the soul that gives you the quest will approach the Dragonborn and teach He/She the spell.

Appearance
Arvak's body is skeletal in appearance, his eyes glow white, and his mane and tail burn with a purple flame effect similar to that found in Bound weaponry.

Find Arvak's Skull
Upon entering the Soul Cairn, along the initial path that leads to the front of the Boneyard, the Dragonborn will come across a frantic Soul calling, "Arvak, Arvak!" He will explain how he and his loyal steed Arvak came to this realm and were attacked by monsters. He had told Arvak to run, that Arvak is still running, and has been for a long time.

He begs the Dragonborn to find Arvak and disappears. Arvak's Skull must be located in the Soul Cairn to free him, although Arvak can sometimes be seen running through the Soul Cairn.

Arvak's Skull can be found due east from the front gate of the Boneyard where Valerica is found. It will be sitting on a pedestal surrounded by ghosts that turn into Mistmen. After obtaining the skull, the soul who was looking for the horse will appear nearby and teach the Dragonborn how to summon Arvak.

Trusty steed
Once the spell to summon Arvak is gained, he can be summoned in either the Soul Cairn, or in the wilds of Skyrim. He cannot however be summoned in any walled cities like Whiterun or Solitude.

When summoned, no experience towards the Conjuration skill is received. If the "Twin Souls" Conjuration perk has been unlocked, two separate incarnations of Arvak can be summoned.

When riding Arvak, it is impossible for the spell to run out. The spell will start to loop, and the "Active Effects" tab counts down from 5 seconds repeatedly until Arvak is dismounted, at which point the spell's effect will count down normally.

He behaves like other summoned creatures, rather than the variety of horses available. For example, rather than staying in one place, Arvak will follow the Dragonborn when not being ridden. If dies in combat, he can be re-summoned. Summoning Arvak and mounting him will replace any currently owned horse, including Frost and Shadowmere. They will, however, reappear after a certain amount of time.

Usefulness

 * Arvak can prove extremely useful if overencumbered and far away from any locations where items can be relieved.
 * Arvak could be used to level various skills, such as striking him with a One-Handed weapon.
 * Arvak can be used as a substitute for the Become Ethereal shout in order to descend long vertical drops unharmed. By summoning and mounting Arvak, then ride off the cliff. Arvak will take much of the fall damage and the Dragonborn will remain relatively unharmed.
 * In the Soul Cairn there are many ruins with bars keeping the Dragonborn out of them, but these can be passed by summoning Arvak through the gate, then activating him. This will cause the Dragonborn to mount Arvak through the gate.

Quests

 * Find Arvak's Skull

Trivia

 * In Norse mythology, Arvak is one of the horses to pull Sol's chariot across the sky, the other horse being named Alsvid.
 * Arvak Is Daedric in origin, as the Oblivion Binding conjuration perk banishes him.

Bugs

 * Riding Arvak while in the Soul Cairn and striking a Keeper with a weapon can result in the keeper being sent flying, and dying upon landing, many meters away.
 * While riding Arvak and swimming, the Dragonborn may be able to dismount and then re-mount Arvak, and the horse will be able to walk and run full speed as if on land.