Okarda'phaa-pattern plasma rifle/Gameplay
From Halopedia, the Halo wiki
In all of the Halo games, plasma-based weapons such as the Plasma Rifle are the best weapons to deplete the enemy shields, especially overshielded players. Although its range limits the weapon to close-quarter and medium range firefights, if used properly a player can quickly dispose of a distant enemy. It is recommended that players use the Plasma Rifles first to eliminate the opponents' shields and finish them off with a human weapon such as the Assault Rifle, Battle Rifle or SMG. In Halo: Combat Evolved, the Plasma Rifle has the ability to stun opponents, enabling players to quickly incapacitate their opponents quickly with a quick melee when close-by. In Halo 2 and Halo 3, dual-wielding increases the combined rate of fire and damage.