The Nightstick is a non-lethal weapon used by police and military forces in Earthrealm.
Officer Kurtis Stryker uses one, befitting his position as a New York cop in Mortal Kombat 3 (and its updates).
Though, the nightstick is only used as a single baton, Stryker uses a pair of Nightsticks in Mortal Kombat: Armageddon. They are fundamentally the same as Jax's Tonfa and Tanya's Kobu Jutsu.
In Mortal Kombat: Defenders of the Realm, it was used to seal portals leading to Outworld.
In Mortal Kombat (2011), he wields the Nightsticks during gameplay and uses it with combos, special moves and his X-Ray Move. However, they were always called Batons rather than Nightsticks in this game.
In Mortal Kombat X, Cassie Cage wields a Nightstick.