notyetagm: I really like the mating line that begins 33 ♖f8+! ♔xf8 34 ♕e7+.
<White sacrifices a whole rook(!) just to be able to double his remaining two heavy pieces on the 7th rank with tempo>. That is, since Black must meet the threat of 35 ♕x♔, he has no time to meet the secondary threat of 35 ♕f7+ and 36 ♕h7# because he must get out of check.
Contrast this with the immediate 33 ♕e7, which threatens only the mate along the 7th rank. Since there is no check, Black needs to meet only this single threat, which he can do with 33 ... ♖g7. This defensive idea ... ♖g7 is not available to Black in the rook decoy line because it does not get the Black king out of check, hence the point of the decoy.
So 34 ♕e7+ forces mate because it lets White double heavy pieces along the 7th rank <with tempo (for free)> while 33 ♕e7 does not force mate because the doubling of the White heavy pieces is not free of charge.