From Halopedia, the Halo wiki
The pulse beam fires a rapid stream of red semi-solid projectiles, apparently composed of crystal or hard light. These projectiles are very similar in appearance to those of the Needler, but do not share the "supercombining" or homing abilities of Needler rounds. Upon puncturing an enemy, the pulse beam's projectiles "shatter" within a few seconds. They travel a considerable range and gradually lose altitude as they fly, giving Enforcers a decent advantage over the Flood as they can fire from long ranges and heights.
The Pulse Beam is designed to effectively combat the Flood by vaporizing the host bodies and Flood forms to prevent reanimation. Due to the sheer amount of projectiles fired at once, and due to the sharpness of the projectiles, the projectiles easily penetrate flesh and most armor.
The pulse beam's rapid rate of fire makes it effective against energy-shielded infantry, such as Spartans and Elites. However, the weapon is easily blown off by concentrated fire, and is also mostly ineffective against vehicles.
Enforcers generally fire pulse beams at infantry units only, saving the mortar weaponry for vehicle based units. When fired, waves of red projectiles are fired towards the Enforcer's enemies. These are difficult to dodge head-on, but can be easily avoided if there is suitable cover, or if the player keeps up a constant pace to the side. The weapon is used only against infantry, as it would be generally ineffective against most, if not all vehicles, as the driver or pilot is generally well defended or hidden from direct view. Therefore, the Enforcer uses it's mortar-like weapon to combat vehicles.
The weapon can easily defeat weak, unshielded units, such as Grunts, and even Jackals can have trouble using their shield to effectively block the projectiles. When used consistently, the weapon can keep an unshielded or wounded enemy pinned down for a considerable amount of time, and can be very distracting and frustrating when trying to defeat the Enforcer. Therefore, it is usually a preferable tactic to disable the Enforcer's weapons first.
List of appearances