Hopefully this helps you it helped me out a lot and I'm looking to square away fellow achievement hunter.
The challenge is anything but simple beat all 20 levels without dying, lucky we don't have to do this in one run.
Now xbox360achievements.org says that the difficulty of this game for a 100% is a 2/10 and it should take you roughly 7-12 hrs to complete.
NOT FOR THIS CHALLENGE.
This is extremely difficult and I finished it today with a total of 32 hrs and 500 deaths.
Now what I did was play the level but every time I came to a puzzle I try to work it out and move forward but if I missed a vine and fell to my death I would just proceed to the end of the level looking and solving puzzles and figure out how I'm going to complete it. After that I would press pause, go down to restart level and attempt it again. I would sometimes spend an hour on a certain level because the room for error is so high.
My best advice is take your time the game is fun and press restart and once in awhile just put it down because I can't begin to tell you how many times I almost put my fist through the wall as you begin to rage.
But in the end it was worth it because most of my friends have this 100% achievements but they do not have this challenge and at the end of the day 100% is completing everything the game has to offer.
Hopefully you go for it and achieve it until then happy hunting.