Father Christmas is a very lazy man. He works one day a year, and spends the rest of his time just sitting there, judging children. What a prick. His elves are the real heroes, and are woefully undersung. For instance, they're zooming around everywhere, adding Christmas cheer wherever they can. Even reaching the obscurity of ACE Team's Rock Of Ages. Now featuring snowballs. You can see some lovely pics of that below.
Jingle jingle, jingle jingle, arenchasickofChristmasyet?
So you've got the skin for the boulder, along with a permanent unlock for all defensive units in all maps, and a bunch of Christmassy tweaks to the interface. And the game is currently 50% off on Steam, at just £3.50 (in the UK, at least). Tis the season to be jolly indeed!