Magic box

A "magic box" was a device resembling a camera which could create models of any object, alter the size of objects, and emit a heat ray. The First Doctor used one to help Santa Claus produce enough toys in time for Christmas, and to create models of the TARDIS, which many children had requested from Santa. The Doctor used a second box to shrink a polar bear, enlarge a squirrel, melt a living snowman, and shrink the Demon Magician. (TVC: A Christmas Story)

Behind the scenes
The Doctor's "magic box" is similar to the Master's Tissue Compression Eliminator in that it can shrink objects, except that it is non-lethal.