is now free to play until 1PM PT on Sunday, December 13th.
The developer also took this opportunity to add daily challenges to the game. Each day offers a random mutator on a random level for you to attempt. Some of these are promised to be "insanely hard for even the most hardcore players out there"!
If you like what you see, you can purchase the full game at 10% off until 10AM PT on December 14th. The game can be downloaded from here