When dragging and dropping a dog into the well during the bonus level, while still holding on to another dog, the newly acquired dog will disappear and the other one and all other dogs in general can no longer be put into the well. You can solve this issue by restarting the level and not repeating the steps that were just mentioned.
Since Felix is a reaper and works for the Ministry of Death, he can only move in the shadows. Felix is equipped with a sun-dial that allows him to rotate the sun. Using the shadow rotation and the environments you move around the board, in order to set people up to die.
For every level competed, a hardcore level is unlocked. Here you can test yourself in time trials and collect skull achievements.