The Very Naughty List (The Very Naughty List Series) by Michael D. A. Clarke

When a down-on-his-luck shopping mall Santa is abruptly fired just days before Christmas, he decides to unleash holiday hell on the staff who wronged him. As the body count rises, shoppers at Merryvale will soon discover that this Santa’s got a bag full of wicked surprises - and he’s ready to deliver!

The Very Naughty List is a wickedly funny, twisted, blood-soaked yuletide horror.