In Rayman Origins and its spin-offs
In Rayman Origins, the player will be rewarded with a Skull Tooth once a Tricky Treasure stage is finished. To unlock the Tricky Treasure levels, a certain number of Electoons indicated by the Fire Teensie must be collected. There are a total of ten Skull Teeth and the player must give them to Mister Death at the Snoring Tree. Once they have all been collected he will open the entrance to the Land of the Livid Dead.
Rayman hugging a Skull Tooth.
In Rayman Jungle Run, Skull Teeth return and are this time awarded to the player when collecting all 100 Lums in a level in one run. 5 of these teeth are needed to unlock the worlds' Land of the Livid Dead level. Like in Rayman Origins, the teeth are given back to Mister Death.