MOUNTED-BACKSTAB

Normally backstabs and sneak attacks cannot be performed while mounted. However, if you learn the Mounted Backstab skill AND are mounted on a shadowy mount, you will be able to attempt it.

Shadowy Mounts are creatures like Nightmares or Shadow Dragons which are able to move with complete silence and are able to shift their shape around in order to permit the backstabber to get into position to land a backstab or sneak attack.