The Alien that Ate Christmas by Stephen Hunt (author of The Court of the Air) is currently free at Amazon (US, ES). This is the product description:
A seasonal short story showcasing Santa, slay-bells and some shocking sci-fi screams!
There are many things you don’t expect to see when you wake up in your bedroom on the evening of Christmas Eve. Santa Claus tied up in a chair and being threatened by an alien was right at the top of young Timmy's list. Sadly for our orphan hero, the alien has plans to save the Earth by giving the planet just what it wants. And that's when the trouble REALLY starts...
This is the illustrated edition, featuring five beautiful interior color illustrations by Stefano Trainito.