¯\_(ツ)_/¯You Cann't shoot The Toad to the other side. You must walk over the zip line.
This was a thing back in the Gloomy Manor attic too. You balance not by shaking the system but by moving it left to right like a steering wheel to balance Luigi.I completed the level and found out what the problem was. I had to shake my 3DS while walking on the rope if Luigi was in danger of falling. I did not know that. In the end, it wasn't that difficult once you knew this. Thanx for your help @KiiWii