Invincible Dog Friend
Visit Falkreath and speak to Lod. Once you accept the task of finding his dog, Barbas, go outside the village and you should locate it. Barbas will then lead you to the Shrin of Clavicus Vile, after which you will receive the 'A Daedra's Best Friend' quest.
Throughout this quest, the dog is invincible, must survive, and can't be killed. This means that you can use him for other tasks, and he will provide a very effective addition to your combat strategies.
Added by: MongooseGeneral Nov 26th 2011, ID#4413