Mate in 2

Black can only move their king, which has a 'star flight' of four diagonal squares. And for each possible king move, we have a corresponding mate:

1...Kd4 2.Nxc6#

1...Kf4 2.Qc7#

1...Kf6 2.Nd7#

1...Kd6 2.Nb7#

Thus, all White needs is a waiting move that maintains these set mates. Initially, any king move seems viable as a waiting option for White; after all, the white king plays no role in the above variations. However, closer inspection reveals that precisely one move, 1.Kb8!, leaves the set lines intact, putting Black in zugzwang. The other king moves, though equally tempting at a glance, are actually tries that meet with unique refutations:

1.Kb7? Kd6! (There is no 2.Nb7#)

1.Kd7? Kf6! (There is no 2.Nd7#)

1.Kc7? Kf4! (There is no 2.Qc7#)

1.Kd8? Kd4! (There is no 2.Nxc6#; the e7 knight is pinned)

Deceptive!