Here's how I use it in game. It is a short missile weapon and because of its awkwardness, the character is at -2 to hit. Range wise I've never set in stone, but I think I would go with 2 short/4 medium/6 for long.
A grappling hook does 1d4 damage. If it scores 4 points of damage it gets lodged into the target. This is where the fun begins. The GM just has to go with what he think what will work. Many different things could happen. Here's a couple of examples.
- I was in a DCC game, I forget the adventure's name, but right off the get go you have to climb a sheer ice wall and once you get near the top a saber-tooth something mauls you. My guy was lower on the climbing rope so I didn't get eaten right away. I had a grappling hook of my own threw it at the saber-tooth something and scored a hit and lodged it into the creature. Since this is DCC I decided my character might as well have a cool death and one of his own choosing, so he held onto the rope connected to the grappling hook and bore all his weight down hoping that extra weight would pull the saber-tooth something plummeting to its death. Would have been kinda cool, right? It didn't happen, but I thought it would have been cool
- It could be used to climb up the backside of a huge beast.
- Used to control the movement of the target. If the grappling hook is set and the player is strong enough or can secure the rope, you got yourself a leash.
The versatility and the creative ways a grappling hook can be used in game is the kind of thing I enjoy. The GM will need to make on the fly rulings, but I don't think it's that difficult to do. Especially for all the OSR GMs, its a cake walk.