A host of CBBC favourites drop in for a huge Christmas special. Hacker stars in A Mash-Up Christmas Carol - his own take on the story of Scrooge - featuring a guest appearance from Zoe Ball. And Roy Wood is in the studio to perform a Christmas classic. Jonny's dad competes against Yasmin's mum in Push Off and there's a slimy singalong. Plus the final two episodes of Dragons: Race to the Edge.