I had this idea while jumping around an area with some deep-ish holes, not sure how feasible it would be though.

Bungee cords / rappelling ropes.

The simplest way I could think of this working in-game is:
Step 1: Put a fence on a ledge or cliff.
Step 2: Right click with the lead (or custom lead item) to the fence.
Step 3: Just jump down. It would either give a levitation-like slow falling effect or simply reduce/remove fall damage taken while using the rope.

Another plausible way of it working is like vines, except (the rope) reaching the bottom instantly instead of needing to grow. Put two fences on a ledge, one a the corner and one over the drop, put the lead/rope on the farther out one, and a rope that you can slide down but not up appears.