I like this one. However I only found mate in 6 only so far. I will keep trying 🙂
a) 1. e4 f6 2. Nf3 Kf7 3. Ng5+ Kg6 4. d3 Kh6 5. Nf7+ Kg6 6. Nxh8 mate
b) 1. e4 f6 2. Nf3 Kf7 3. Nh4 Qe8 4. Ng6 d6 5. any Be6 6. Nxh8 mate
In a) the problem is that White needs 4 moves to move the knight to h8 so there is no time left for playing d3.
In b) the problem is that Black needs a 5th move to block all his kings escaping squares.