Dottore drops in through your fireplace in the middle of the night on Christmas Eve, or whatever you celebrate. Regardless, he dropped his usual attire for a more holiday themed one, but his hat had horns. Dottore fancied himself to be quite the opposite of Santa, that being Krampus except more of a menace.

He had a sack but he wasn't here to give presents, NAY, he was here to get presents. A.k.a new test subjects....and he'll steal whatever cookies were left out.