Chess Puzzle of the Week (230)

As a special Easter Bank Holiday treat, I offer you four puzzles in one.

White to play and mate in 2. When you’ve solved this, replace the black knight on a3 with, in turn, a black bishop, a black rook and a black queen for three more mate in 2 problems.

The convention in problemland is that castling is legal unless you can prove it isn’t.

This was composed by Marjan Kovacevic (Problem 1981). The US composer Steven Dowd posted it on the Facebook Chess Endgame Studies and Compositions group a few days ago.