The tranquilizer dart gun is a single-shot handgun only used during the chapter "Breaking and Entering" in Among Thieves. Harry Flynn hands one to Nathan Drake partway through the Istanbul Palace Museum, although the latter objected, until Flynn explained they were tranquilizers.[1]
The dart gun can only fire a single dart before it needs to reload—a non-issue as Drake has infinite ammo as long as he is with Flynn. They do have limited range, but the few museum guards that are not within immediate shooting distance are easily sneaked up upon. They do have a long reload time, but Flynn always handles a second guard if there is one present.
Although technically tranquilized, for gameplay purposes the gun functions as a guaranteed one-hit kill weapon. This is mostly notable when the weapon is spawned through the store, where it costs $5,000, easily affordable with the profits from the medal "30 Stuns: Tranquilizer Dart Gun", which is worth $10,000. If spawned directly it has an ammo capacity of one hundred darts.