Cactus

 is a gun that fires low-damage needles rapidly. Its high ammo, fast rate of fire, and infinite range make it a good room clearer, especially for earlier floors.

Trivia

 * 1000 Needles! is a reference to a move used by the Cactuar, a recurring enemy from the Final Fantasy series, who resembles a walking cactus.
 * The "undiscovered Chamber" in the Cactus' description may be the unused Old West floor.