M90 Assault Shotgun

Advantages
Since the shotgun fires 15 spreading pellets per shot (in Halo 2, it fires fewer pellets and in random amounts), the combined force of each relatively weak pellet does a significant amount of damage. Its high damage potential makes it effective against any Covenant unit (even the Hunter, if shot in its exposed back), but only if the player can get close enough to render the gun effective. The shotgun can also be used, though not necessarily effectively, against all manner of vehicles, and many players consider it the ideal weapon with which to destroy Banshees which happen to be within the shotgun's effective range. In addition, this weapon is extremely effective against all forms of Flood at short and medium ranges. The shotgun also reloads in a different manner than the rest of the weapons in Halo. Each round is put into the shotgun, one-by-one, so reloading all twelve shells at one time may take a while. However, the player may interrupt the reloading process at any time and fire with however many rounds are currently loaded into the weapon. Another popular way of firing the shotgun involves inserting a shell, firing, and then inserting another shell, etc. While this takes slightly longer, it has the advantage of always having eleven shells chambered. Apart from that it is devastating in close combat.

Disadvantages
Although many skilled players are able to hit a target at almost any distance using this weapon, the shotgun's greatest limiting factor is its range, making it useless in any wide-open terrain. Ammunition for this weapon is also sometimes difficult to come by in single-player.

Halo : Combat Evolved

 * The Shotgun can best most medium range weapons in normal matches. Don't be afraid to lay it on while using cover, the 12 rounds last longer then you might think.
 * Lead your target in the PC version. In the Xbox version this isn't a problem.
 * Use the POP tactic.[[Image:POP_Tactics.JPG|right|thumb|500px|Diagram of POP tactics, an effective way to score a kill when being pursued.]]As in this diagram, use your corners and the element of surprise. Most enemies don't think that you will "pop" back in your weakened state. Plus, only above average players can react to something like this. The trick is timing. Too early, and you get killed, too late and they gain the edge. Grenades can also help in this situation.
 * When attacking, try to sneak up to your destination. It's easy to score kills on unprepared people, especially if they're clumped up, say, around a flag. Throw grenades to soften targets before you enter, if they know you're coming. This is true for most weapons, but a shotgun expert can get shields down, and kill people 1 by 1 (much like turkey hunting), using cover and popping out multiple times.

Halo 2

 * The shotgun is significantly weaker in Halo 2. It's ROF is decreased, reload time increased, and its range is lessened. However, there are a couple things to keep in mind while using this weapon, to make the most of it.
 * The shotgun is your best defense against the sword, time your shots right and they'll never be able to touch you. However, In XBL, lag can make this ineffective.
 * You will almost always need to follow up a shot with a melee attack, simply because most players aren't stupid enough to let you get close. The lunge feature in Halo 2 makes this work well against most enemies.
 * Timing is everything. Always get closer then you think you should, because the shotgun can only get a kill shot in under 5 feet. (read:point-blank. this is strange because all of the pellets still hit the target at longer ranges, but it still does less damage) If you usually follow up with a melee though, different timings are needed. Some people switch to "boxer" button settings in all shotgun matches.
 * Never reload unless you have a good 5-10 seconds, depending on how many shots remain in the magazine. In Halo 2, the shotgun takes an extremely long time to reload.

Influence
The mechanical design of the M90 shotgun is loosely based on the South African Neostead shotgun which features dual six-round top-loaded magazines. Its pump mechanism operates in a forward-back motion, due to its rear-load configuration (rather than normal back-forward motion). The weapon features two integral tube magazines with a total capacity of twelve rounds (6+6+1) and ambidextrous bottom ejecting shells. It is chambered for standard 12-Gauge 2.75-inch cartridges. The aesthetic design is a composite of multiple pump-action designs.

Multiplayer Role
The shotgun's effectiveness in multiplayer games varies depending on the terrain; indoors and in tight spaces, it is considered by many players to be the weapon par excellence. Many players carry the shotgun and a long range weapon, such as the Pistol or Battle Rifle, thus making for a more flexible arsenal. Continuous firing by using the magazine and loading one shell then firing does not affect the rate of fire significantly, prompting a few players to employ a tactic dubbed "shotgun sniping" as suppressive fire across medium-sized maps. On the Internet, many games are shotguns only, with most of these battles being set in the map Battle Creek (Level).

Appearances
The Shotgun appeared in Halo. The shotgun had blue sights on the tip and top of the weapon. In Halo 2 the color changed to green. It also appeared much blacker. This weapon is to return in Halo 3. It also seems to have returned to the original blue lights on the sights, although from the ViDoc Et Tu, Brute?, it returns the feature of blue iron sights from Halo with a added flashlight to the foregrip. And it features Halo 2's flat black color.

Effective Against
All Enemies and Vehicles except Brutes as the small fragments of the shells lack the punch to tear through the Brutes thick hides. It may be possible to one shot kill a brute in Halo 3 acorreding to the video above