Solution to Helpmate Number 6
The theme of this problem is the same as for helpmate number 5 namely selective promotion followed by self-block or interference by the promoted piece (further details on this theme can be found in the solution to helpmate number 5).
Solution 1.
Black moving first
1.d1=N Bc2 2. Nb2 Be3 mate.
Solution 2.
Black moving first
1. d1=R Bc2 2. Rd2 Ba3 mate.