Fuel Rod Gun
From Halopedia, the Halo wiki
(PC/Mac Multiplayer Only) Rate of fire: Average (2 round per second) Damage per hit: Very high Range: Medium Accuracy: Low-medium Magazine size: 5 rounds per clip Maximum ammo: 30 rounds
Advantages
This explosive gun is a requirement for all Spartans and Elites worth their ass. Unlike their Halo counterparts, they don't have failsafes that make them blow up as soon as you drop them. Fuel rod guns are now magazine-fed, and holds five rounds each. Two to three rounds is enough to blow a Hunter to oblivion. The gun fires fairly fast, and reloads at around the same rate as the rocket launcher. Another similarity is that it has a 2X scope.
Disadvantages
The battery is the same one as used by the Plasma pistol/rifle, so it runs out of power fairly quickly, and is subject to overheating. It may also hurt or kill the user if fired at close range. Its accuracy is much like the plasma rifle's, very accurate at cool temperatures but very inaccurate as heat reaches maximum. There are also very few per map (in a map like Blood Gulch for example there is only one). The huge green projectiles leave a faint green trail which can give away your position, and it obstructs your visibility when carrying it due to its size. Finally, it takes two to three direct hits, as opposed to one with the Rocket Launcher, to kill an opponent.
Hunter
There are the ones that the Hunters use which shoot out long beams of fuel rod. If only we had some way of taking that gun off a Hunter and use it for ourselves..."sigh"
Multiplayer Role
The ultimately annoying weapon, this can wipe out whole groups of enemies with a few shots and can bombard enemy bases from far away. If used in closed spaces it is devastating, and can be used as a substitute for the Rocket Launcher if in a advantageous position. A player with this weapon can become an unstoppable juggernaut with good cover/backup. Good for CTF and Slayer.