Name: Grappling Hook P/W/C Type: Courage Appearance: A thirty-foot rope, and a grappling hook at one end. Description of Function: The user can throw the grappling hook to grapple on to the target area. For example, a person may throw the grappling hook at a roof, in which it will catch hold of the roof, allowing the user to climb up. Another use is to throw it something (a tree limb, a rock, etc.) protruding above a gap, where the hook will wrap around it, allowing the user to swing across. If the user has a certain amount of courage, the user may throw the grappling hook at a creature or other NPC to have five rupees attach to the hook and be brought back to the user. Limitations: The user is allowed to steal rupees from a creature or NPC once per quest.
For the most part, a grappling hook is a common tier object. It's a long length of rope with a weighted hook or claw at the end, and therefore on its own isn't enough to be made as an actual Treasure. The only reason it would be is because of the other function you propose for it, that being the rupee theft per quest. However, we already have a treasure that fulfills this exact function: the Rupoor Supply, which allows a character to acquire an extra five rupees per quest.
Yeah, common-tier items are anything from washrags to bows. Making a list of them would be too long. TC is for magic-tier items. The introduction post to the Library of Treasures explains the different tiers pretty well, if you haven't already seen it.
