To the description, why not: "0: Your weapon attacks a random enemy target when replaced by another weapon."
Well, with this card you have to build your deck around it. So, these weapons may be your main source of damage, and they deal damage only once, and you can't choose the target. Double of it's attack sounds far better.
Does the damage bonus of Hammer, Short Bow and Dagger count when using the right mark? It should in my opionion.