Nightrider (chess)

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f4 white pawn
d3 black cross
b2 white upside-down knight
d1 black cross
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The nightrider (represented by an inverted knight) makes any number of knight moves in the same direction.

The nightrider, alternatively spelled knightrider and also known as the knightmare or unicorn (though the latter term sometimes refers to the bishop+nightrider compound), is a fairy chess piece that can move any number of steps as a knight in the same direction. The nightrider is often represented by an altered version of the knight's icon.[1] In this article, the nightrider is represented by an inverted knight and notated as N; the knight is abbreviated as S for the German name Springer.

The nightrider was invented by Thomas Rayner Dawson in 1925. It is often used in chess problems.