Ever since I was a kid I've thought of this kind of thing, just my mind wondering. I even devised a human version for use in Earth! Well it only works at sea! Imagine a lance like a medieval jousting lance that curved taper to a wider conical cross section at the handle end, well turn that vertically and have a skydiver riding this thing like a pogo stick! So I thought that if you can get that curvature right and the whole thing scaled up the tip can hit the surface of the water at full terminal velocity and the whole thing will rapidly reduce velocity as more of the lance enters the water as both the resistance due to friction and floatation will increase from almost nothing (all determined by the curvature and dimensions of the lance) it will take a certain amount of 'commitment' from the skydiver!