Type-33 needler

Stats Rate of fire: Average to high (3-10 per second, increases  with continued fire) Damage per hit: Low to very high (Explosion will occur per 7  needles in target) Range: Short to medium (most effective at short range) Accuracy: High (Needles are homing) Magazine size: 20 needles (30 in Halo 2) Maximum ammo: 90 needles (including fully loaded magazine)

Advantages
This weapon fires enemy-tracking needles that embed themselves in the flesh of a target before exploding to cause damage. Rate of fire increases with continuous fire. If 7 or more needles accumulate in the target the needles' combined strength will create a large explosion, killing the target and causing splash damage to other nearby enemies. Needles can penetrate the energy shields of Elites, Sentinels, and Spartans. They are especially useful against Brutes (who have no shields) in Halo 2's Campaign mode.

When dual wielded, the effectiveness of the needlers can be increased by firing them "out of phase". This is accomplished when the user begins firing one of his needlers a fraction of a second before the other, and continues to fire them in full-auto so that the shots from each weapon are fired in a "one-two punch" pattern (you can tell when the pattern is just right because the guns will sound as if they are firing much more rapidly). This allows for a more constant and consistent stream of fire (since each needle is in it's own slot in the sequence, the failure of one needle to connect no longer means that two will fail) and also adds to the weapon's psychological impact in multiplayer.

Insightful players will find the needler can be the key to victory in certain situations. For instance, on the level "Keyes" in Halo 1, players will encounter three or four Flood combat forms situated on ledges above the player. Rushing through means dying in a gauntlet of fire from an elevated position. Grabbing a needler and firing at each Flood from behind a conveniently located stationary shield will allow the player to safely destroy each enemy. Furthermore, each Flood is positioned in shadow making it extremely difficult to effectively engage them with other direct-fire weapons; the needler solves this problem by homing in on these otherwise nearly invisible enemies. They can also be effective against Elites by either killing them outright or forcing them to dodge or retreat, giving players a chance to reposition themselves for an advantage.

Disadvantages
The needles are slow, and are not effective against vehicles. The needles also take time to hit/explode on the target, leaving the target time to move in and inflict some of the explosive splash damage on the shooter. It is nearly impossible to hit invisible Elites with the Needler, as they do not home to camouflaged targets. The learning curve of the "lead" needed to hit strafing targets is also high. And when faced with experienced opponents in multiplayer (who often randomize their strafing patterns) the weapon is almost always overshadowed by better, more reliable options.

Influence
The needler was inspired by the Flechette gun from the Marathon series.

Appearences
The Needler first appeared in the original Halo: Combat Evolved. It made a return in Halo 2, and was made slightly more powerful with the advent of dual wielding. However, after Halo 2's 1.1 multiplayer patch, the weapon was toned down. The weapon is set to return in Halo 3. This time it will not be dual wieldable, but Bungie has stated that the weapon will be significantly rebalanced to allow it to stand on it's own.

Effective Against
Elites, Grunts, Brutes, Sentinels, small groups of tightly packed Flood.