Okay, this was a trick question, which admittedly is not very Christmassy.

It must be Black’s move; if it were White’s then there’s no legal move that Black can just have made. But on any Black move, White can now mate immediately:

1. … Kxb7 2. c8=Q#
1. … Bxb7 2. Na7#
1. … Rxc7 2. R(1)xc7#
1. … Rd8+ 2. cxd8=N#

On anything else, White plays 2. Rb8#.