Cerberus

Cerberus is a firearm. It can only be equipped by Noctis, and it allows the player to use snipe mode.

Source
Cerberus can be obtained as a drop from MA Veles-bis (10% drop rate). It can also be found as a collectable in the northeastern sector of Fort Vaullerey, just inside the small building tucked into the base's corner.

Gameplay
When equipped and selected, Cerberus can be fired like any other firearm by tapping the attack button (O on PS4 and B on XBOX 1). Snipe mode is activated by holding either R1 and Triangle for PS4 or RB and Y on Xbox One. In this mode, a first-person view of crosshairs with a pulsing red dot at its center appears. The player can use snipe mode to break a target's appendages from afar and land critical hits with headshots. The sniper's range is 100ft.

Trivia

 * In Greek mythos, Cerberus is the three-headed guard dog of the Underworld.
 * There is a creature in the FFXV universe named Cerberus that only appeared in Kingsglaive and Omen before it was patched in for Royal and Windows Edition.
 * Vincent Valentine (from FFVII) wields a revolver called Cerberus in both the Dirge of Cerberus game and the Advent Children movie.