"The solution is a real shocker! " Too much of a good clue.
First looked at 1...Rxd2 (that's a real shocker) 2.Nxd2 Bxf4.
Bit of fun if the Rook defends the Knight (3.Rd1) with the Rook but that
did not appear forced infact it's bad.
Only other shock move that looked like it was on was 1...g5 and then
with the clues I saw in the Rxd2 line I saw the mess the Rook was getting in.
Would I have seen it OTB. No chance, not enough King in it for me.
My forte is mating Kings. Them I rarely miss.
What would I have played. Most likely 1...Bd3 going for Be4.
Then the f3 Knight is pinned against g2 and that is a big check.
The King....I always go for the King.
"....but if I put it in a tactics book, it would be in the most difficult category."
No. (the difficult chapters never get read)
The book will be tactical puzzles to solve and the hard ones will come in with
the easy ones. Just like it happens in real OTB play. You don't know what to expect.
A bog standard win of a piece followed by a sac sac mate followed by a
pawn promotion trick followed by an exploitation of weak back rank etc.
I would not use this one.