I was gonna make it "Winter Sans-ta" ..but it didn't feel catchy nor funny.
Ahh the festive preparations have begun! How's your holiday preparation going on?
Anyhow, this is Sans doing his deed of being Santa for Christmas.
Yep, this is actually canon. If you've played the game enough, you'd know Papyrus has action figures.
He says he gets them from a short chubby man with a wide smile, claiming it's Santa Claus.
If you're able to unlock Sans' room by doing the loading trick you can find letter on the floor.
They are addressed to - SPOILERS - Santa Claus.
Yep, blew your mind, didn't I? If I didn't ..at least you like the picture right?
Anyhow, I've got more to offer this winter for you yanks - summer for my Australian friends :L
Till then chaps~