The Santa's Little Helper was a Gifting Event similiar to Get the Power of the Ancient. It required the Mission Items Santa's Sleigh, Church Bell, and Mistletoe. You have 14 days to complete the ability set. The event began on December 20th 2011 and run until January 3rd 2012.
Collecting the Merry Trinkets
(T)he season to be jolly takes a sinister turn. Master the twisted traditions and Santa's Evil Helper will be yours to command.
You must collect 30 of each item to complete the ability set.
Each ability had 3 levels of mastery and by mastering all abilities earns the ability Santa's Evil Helper.
Mythology and Etymology
The Simpsons' pet greyhound which they adopted on Christmas Eve is named Santa's Little Helper.
See also: Gifting Event