EDIT 30.7.2013: The original video was marked as private on Youtube so have replaced it accordingly. The new video is obviously for PS3 however the level and boss plays exactly the same.
This simply expands on JUPIDUR's solution, with a video walkthrough for this final level. This achievement has many pre-requisites so lets get started.
In order to even open the level 'The Land of the Livid Dead' you will need to collect the 10 Skull Teeth throughout the game. Each skull tooth level is accessible after collecting a certain number of Electoons, the final requiring a total of 200. Luckily you won't need to perfect all levels to get this, but for most people you might finish the game first before this happens.
Each chase level requires you to keep up with the fleeing chest, holding RT to run continuously to keep up. These levels aren't too taxing but do require some perseverance. Once you have all 10 skull teeth, you'll have netted the following achievements:
Now head to the Snoring tree and return the teeth, heading through the portal on the left. This level is extremely frustrating with the pace hard and fast with no hearts and few checkpoints. Just keep going and this achievement will pop right after the boss (which after finishing the level feels remarkably easy).
See below for the Youtube video uploaded by ILLZEBRAlol (with the deaths edited out) which covers the final tooth, the final level and boss, all credits to him for the vid.
If anyone has any ideas to improve this solution please post a comment instead of voting negatively and we'll improve this together. best of luck!