The game is called "Monster 4" and its set number is 3837. It's basically a variation of Tic-Tac-Toe on a 4x4 grid with various extras such as jokers and a spider.http://shop.lego.com/product/Default.aspx?p=3837
The building instructions
can be downloaded from the customer service page if you want a closer look. There is a second booklet with the gameplay instructions, but it seems they don't have those online.
There are five different heads - the white evil skeleton and green troll heads are the same as in the regular castle sets. The three new heads are a brown "zombie", a red "devil" and an orange "evil pumpkin". I myself have used the pumpkin to make a dark-side Ahsoka
(as a joke). I'm not sure what use the zombie or devil could be put to as they look a bit too cartoonish.
EDIT: Missed the link to Flickr when I first read your post. His Darth Lycanus
is using the brown head which I termed "zombie". I guess it could indeed be a mutant Chewie... Darth Infernus
is the red "devil" head (it has horns). I think the pink tongue spoils it. Why would a Sith lord be blowing raspberries?