1.c5
If 1...Bxc5 then 2.bxc8=Q and 3.Qxd7 is unstoppable
if 1...Nxc5 or 1...Rxc5 then 2.bxc8=N and 3.Nf8# is unstoppable.
Yes, i just came to that conclusion.
Oops, just noticed Loomis mentioned the problem with Nxe4.1.c5 Nxc5 2.bxc8=Q Nxe4 3.Qxd7#
1.c5 Rxc5 2.bxc8=N Nc3 3.Nf8#
1.c5 Bxc5 2.bxc8=Q Nc3 3.Qxd7#
Another variation......last move Nxc7 check mate!
I already posted that variation! 
1. c5 Nxc5 2. bxc8=Q and black should just leave the knight on c5 since it defends d7. I don't see a checkmate after 2. ... Ra5.
But this line I like. 1. c5 Nxc5 2. bxa8=B and now the Bishop on a8 covers d5 so Nxe4 is not a problem and Nxf7 is coming.
Do you mean Nf8? There isn't a Nxf7. If Nf8 then Ke7
Ah. Still leaves a hole on d6.
Ok. I think I got it now:
here are all the variations
1.c5 Nxc5 2.bxa8=N Nxe4 3.Naxc7#
1.c5 Bxc5 2.bxc8=Q Nc3 3.Qxd7#
1.c5 Rxc5 2.bxc8=N Nc3 3.Nf8#
1.c5 bxc5 2.bxc8=N Nc3 3.Nf8#
Added the Bxb7 variation:
1.c5 Nxc5 2.bxa8=N Nxe4 3.Naxc7#
1.c5 Bxc5 2.bxc8=Q Nc3 3.Qxd7#
1.c5 Rxc5 2.bxc8=N Nc3 3.Nf8#
1.c5 bxc5 2.bxc8=N Nc3 3.Nf8#
1.c5 Bxb7 2.Ng7+ Rxg7 3.Rd8#
I missed your message. bxc8=N. wo'nt work? ans: Rxc8
1.c5
If 1...Bxc5 then 2.bxc8=Q and 3.Qxd7 is unstoppable
if 1...Nxc5 or 1...Rxc5 then 2.bxc8=N and 3.Nf8# is unstoppable.
Yes, i just came to that conclusion.
Oops, just noticed Loomis mentioned the problem with Nxe4.1.c5 Nxc5 2.bxc8=Q Nxe4 3.Qxd7#
1.c5 Rxc5 2.bxc8=N Nc3 3.Nf8#
1.c5 Bxc5 2.bxc8=Q Nc3 3.Qxd7#
Another variation......last move Nxc7 check mate!