Solution

3) Two solutions: Helpmate in three. Black moves first.

a)

1...Ke5
2.e3 Nf6
3.Rd7 Nd6
4.Re7

b)

1.Ke6
2.e5 Nd6
3.e4 Nf7
4.Re8

The second mate is shifted one square further up the board. Another chameleon echo.