Grade C-
Certainly not obvious moves

White's Rook guards g2 against ...Q×g2#.
Therefore moving the R to another rank must be to give check, furthermore, every move must continue to check until mate, lest ...Q×g2#.

1. Rf8!+...K×f8 (forced)
So far, so good, but can checks be sustained?
2. Qh8+...Kf7 (forced)
White must keep BK confined!
BP @g7 is all ready attacked by WB @e5...
3. Q×g7+ removing the obstacle! ...Ke8 (forced)
4. Qg8#

Each Black reply is forced, and therefore predictable.
But visualizing the whole process is necessary before making the first move: 1. Rf8!+, lest ...Q×g2# ends it all the other way! 🤔

The need to anticipate 4 moves in advance makes 1. Rf8!+ an excellent move!

Looking back, I recall having been overly concerned with g6, a square that W only covers with his Q, and if this Q moves away, g6 becomes available for a flight square. In the end, 3. Q×g7+ covers g6 just in time to prevent it from being Black's escape path.