Why doesn't the purple gargoyle break the glass in the level 'The Dark Tower'?
Towards the end of the level 'The Dark Tower' you will be required to use a purple gargoyle to break a pane of glass. On some low performance machines such as Mac Minis and MacBooks you may find that the glass doesn't break as it should. To get around this issue navigate to Options → Video Settings, and set the option Enhanced Graphics to OFF.
You will be required to restart the game in order for this change to take effect, but when you retry the level the glass will break.