Santa on a rampage
The previously announced holiday add-on content for Saints Row IV, How the Saints Save Christmas, has been released along with this delightful trailer which explains the premise. Simply put, Santa Claus is apparently some kind of horrific monstrosity who plans to put all of the universe on the naughty list and only the Saints can stop him.
For my money, the best "evil Santa" in entertainment is the one found in Futurama, but I'm open to the possibility of that interpretation being unseated. Those antlers are pretty horrifying.