Solution:
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1.♗b2! ~ 2.♖c1 ♖×b4 3.a×b4 ~ 4.♖d1#
1...♘d7 2.♘c×b5+ ♔d5 3.♘c7+ ♔d6 4.♖d5+ ♘×d5 5.♘c8#
1...♘e6 2.♘×e4+ ♔d5 3.♘×f6+ ♔d6 4.♕d5+ ♘×d5 5.♘c8#
1...♖×b4 2.♖×a6 ~ 3.♖d6+ (Sa2+, S:e4+, S:b5+, Sa4+, a:b4)
2...♘c6 3.♘×c6+ ♔c5 4.♘×e4+ ♔d5 5.♘×b4#
1...♖×a3 2.♖×b5 ~ 3.♘a2# (Sc~#)
2...♖×b3 3.♖c5 ~ 4.♘cb5#
3...♖×b2 4.♘cb5+ (Sab5+) a×b5 5.♘×b5#