Ah i see, wasn't going back to the Start but there's another whole section on the top.
The Boss seems quit hard, after 4 tries i gave up since you have to start all over again, you might wanna give some "Waypoints" like when you get a PowerUp the Progress gets saved.
The Climbing feels to slow and sluggish after a couple tries, so it makes no fun to get to the Boss again.
But i like the Climbing mechanic switching from one side to the other side to get higher, cool solution.
and Still like the Visual appearance.