The Grappling Hook is an item introduced in Rise and Swine. It can shoot a toilet plunger (default) into any surface, so that the vehicle would swing across gaps rather than falling into them, and is also used to go up. Grappling Hooks also have some destructive capabilities, as they can also break your machine and knock your pig out of the box that it is in. As of Custom Contraptions,this was fixed. They can also sometimes ignite/detonate TNT. If the grappling hook is fired, quickly tapping the fire button or the hook body itself can retract the hook.
It looks like a toilet plunger with a string attached onto it inside a gun.
As mentioned before,it was fixed since update 2.0,so the capability of damaging vehicles is gone,and sticks to them instead,but the alien version still functions as a weapon, and the Detacher is better at breaking off certain parts of the vehicle.
This item was the third item released in Rise and Swine, which weirdly is now the second episode,not fourth.
If the grappling hook is facing a box, it will hit it and launch it into air instead of grabbing the landscape, which makes it a good vehicle booster. Patched in 2.0.
If the grappling hook hits a TNT crate that was part of the landscape, the TNT will explode, but the grappling hook will remain attached to the spot where it hit the TNT.