Mates to squares blocked by white units

1.c7? zz
1...Kd3 (b4), bxc4+ 2.Bc6#, Bxc4#
1...Kc5!

1.e5? zz
1...Kd3 (b4), Kc5 2.Be4#, Qb6#
1...Kxe5!

1.c5? zz
1...Kd3, Ke5 2.Bc4#, Qh8#
1...b4!

1.e7! zz
1...Kd3 (b4), bxc4+, Kc5, Ke5 2.Be6#, Bxc4#, Qc6#, Qh8#

4-phase change of mate after 1...Kd3. There is also the creating of weaknesses in white position leading to refutations in 3 tries, that adds a bit of interest.

1.Rg8? zz
1...Sb5 (Se2), Kd4 2.Kd7#, Rg4#
1...Sd5!

1.d7? zz
1...Se2, Kd4 2.Kd6#, Re4#
1...Sb5!

1.Qd7? zz
1...Sb5, Kd4 2.Ke7#, Qa4#
1...Sd5!

1.Sd7! zz
1...Sb5 (Se2), Kd4 2.Kf6#, Qh4#

Change of 2 mates in 4 phases! Of course, there are banal duals after "weak" moves of knight, e.g. after Sb1 in all phases, but that doesn't matter. Main trick is in the fact that 3 keys simultaneously unblock and block square for wK, pawn, queen and knight arrive at d7. Changed mates after king move are ingeniously arranged too. Two minor flaws: 2 tries are refuted by same move, Re8 plays only in 1st try, then it sleeps.

1.Sb6? th. 2.Qd4#
1...Be6, Qxf6, Sxf4, Sxb4, c5, Rxe7
2.Qxe6#, Sxc8#, Qxf4#, Qe5#, Qd5#, Qxe7#
1...Bxc3!

1.Qd4! th. 2.Sb6#
1...Be6, Qxf6, Sxf4, Sxb4, c5, Rxe7
2.Se4#, Sxf6#, Sxf4#, Sxb4#, Rb6#, Sxe7#
1...Bxc3, cxd5
2.Sxc3#, Qb6#

The things are little bit crowded around black king and it is mainly lack of space that motivates unexpected change in 6 variations (!) after key and threat reciprocally inverted (!!! - it is possibly the only twomover with this blend of themes - am I right?). In this composition it isn't white who frees squares for lethal mating moves, no, it is black who annihilates blocking white pawns.

1.Rxe3? zz
1...bxc6, gxf3 2.Bxc6#, Bxf3#
1...Bxe6!

1.fxg4? zz
1...exd2, Bxe6 2.Bf3#, Sf3#
1...bxc6!

1.cxb7? zz
1...exd2, Bxe6 2.Bc6#, Sc6#
1...gxf3!

1.Rf6! zz
1...bxc6, gxf3 2.Sxc6#, Sxf3#
1...exd2, Bxe6 2.f4#, Rxe6#

How simple and how efficient! For any of 4 thematical mates Sf3, Sc6, Bc6, Bf3 two of 4 actions must be taken: f3 vacated, potential flight at e6 covered or blocked, c6 vacated, Re2 activated to e5. All keys take care of one of these and white then waits how will black harm himself. In tries one of 4 black defences is removed, so black wisely selects one for refutation, two other are met by above given mates. In solution, however, all 4 black defences are in existence and these two that aren't harmful in expected manner, are followed by completely new mates made possible by special key. Again, how simple and how amazing!