The queen is pinned so there is no Rd4+
To prevent Rd4, Nf3 and Bb2 must be used.
The knight on e2 is overworked.
The answer is Rf4!
Nxf4, Bb2#
Nd4, Nf7#
f5, Qg7#
Kd4, Qxd6#
else, Nf3#
To prevent Rd4, Nf3 and Bb2 must be used.
The knight on e2 is overworked.
The answer is Rf4!
Nxf4, Bb2#
Nd4, Nf7#
f5, Qg7#
Kd4, Qxd6#
else, Nf3#