Rulings and Errata
A Hero can equip the Short Bow even if the Monster you attack is not in Rank 2 or 3. If an Archer equips the Short Bow, the bow’s total Attack bonus is +5, but only against a Monster in Rank 2 or 3. Neither bonus applies in Rank 1.
Currently, this card does not give a bonus when equipped by Thunderstone Advance's rangers.