-1.g2xPf3 & 1.Rxb7 ~ 2.Rb8.
Balance of white captures vs. black units:
7 black units on board + gf + fg + cde + defghg (to promote Ba2 w/o distrurbing black's castling) + Bf8 = 17, so black can't castle. (The promoting pawn must have passed thru d7 or f7.)
(8+7) White retracts one move, then mate in 2.
Günther Weeth, 2014