Multiple Batarangs

Batman uses Multiple Batarangs to assist him, and threw two or three Batarangs at once, which allowed him to hit multiple targets.

Batman: Arkham Origins
The Multi Batarangs could be used once an upgrade was purchased.

Batman: Arkham Asylum
The player could upgrade the normal Batarang to unlock the Twin Batarang, where Batman could target two enemies at the same time. After you obtained the Twin Batarang, you could upgrade it to the Triple Batarang, where Batman was able to target three enemies at once. The upgrades took priority when used during Combat, provided that the player had unlocked the Combo Batarang.

Batman: Arkham Knight
They reappeared in Arkham Knight. From the beginning of the game, they appeared when quickfired in combat, but required WayneTech Upgrades in order to be aimed. That time, however, they didn't appear on the gadget wheel, but were instead chosen by aiming the Batarang and pressing R1/RB.

Trivia

 * They also appeared in Batman: Arkham Origins. Unlike Batman: Arkham Asylum, only one was thrown when quick-fired.
 * However, the Freeflow Focus Power Gadget upgrade in Batman: Arkham City and Batman: Arkham Origins allowed Batman to unleash three Batarangs when he was in combat.
 * In Batman: Arkham Knight, Batman would switch to smaller Batarangs when using the Multi-Batarang. During combat when used as a freeflow gadget, Batman would use the regular sized Batarangs. In Arkham Origins and Asylum, Batman would use the normal sized Batarangs as well.