Meisterwerke

If black may castle, then his last move must've been b7-b5, because c6xb5 requires too many captures (Bc1 was captured on his home-square). So #2 with 1. cb6 Kd8/c6 2. Qf8#. If black may not castle, then #2 with 1. OO ~ 2. Rf8#.

Solution by Philippe Schnoebelen