A nightrider (also known as a knightmare or unicorn) is a fairy chess piece that can move (proportionate to how a knight moves) in any direction. For example, a nightrider on b2 can reach square c4 and forward to d6 and e8, but cannot jump over pawn f4 to h5. The nightrider is usually represented by an inverted knight on diagram and symbol N in text, in which case the knight is abbreviated as S for German Springer. Nightrider was invented by T. R. Dawson in 1925. Nightrider is used mostly in chess problems.
Nightrider can also give triple check.
The king together with two knights cannot win endgame against a lone king (KSS vs K), but the king together with a knight and a nightrider can win, because the knight cannot win a tempo, but the nightrider can.
Solution: 1. Ne7! Ka7 2. Ng3 Ka8 3. Ne4 Ka7 4. Sb5+ Ka8 5. Nd2#