The Unggoy serve as a prominent enemy in all of the Halo games.
The Grunt can use any sort of weapon that is designed to be held in one hand. In some situations grunts have been seen to use heavy artillery weapons, such as the Fuel Rod Gun. So, on higher difficulties, the Grunt can prove to be a dangerous enemy to the Player and his allies.
Grunts usually fight in groups consisting of mostly Minor Grunts, one or two Major Grunts, and an Elite leading them in Halo: Combat Evolved and Halo 2 or a Brute in Halo 3. Most of the time, when the Elite or Brute leading them is dead, the Grunts will run away, even the higher-ranking ones. Grunts have a typical tactical style in combat, which the Minor Grunts combine their firepower for softening and lowering their enemies health, body armor or shields, so that the Major Grunts, Elite or Brute leader will easily kill or quickly finishing off enemy units. A group of Grunts are mostly used to slow enemy advancements or do as much significant damage as possible to weaken enemy forces and forced to waste enemy ammunition on themselves or simply used as cannon fodder.There are times they take advantage of their size, they can easily hide and ambush or surprise their enemies with a hail of plasma fire.
Grunts can be tenacious fighters as long as they have someone leading them. Higher-ranking Grunts may not run away, but instead, keep fighting you. The Covenant think of the Grunt race as only cannon fodder and do not care how many of them die in combat. Grunts make tactical mistakes, such as throwing a grenade too near to themselves, or turning their backs and running away, allowing for a quick kill. They are very vicious little creatures and when they are determined and have motives they can be deadly especially when lead by a higher rank although they can lead themselves. Occasionally, mentally unstable grunts will attach two plasma grenades to themselves and rush at you, which kills the grunt and can kill you on any difficulty.
Grunts are often armed with the ubiquitous Plasma Pistol, although they are often seen wielding Needlers and Fuel Rod Guns. Occasionally, Grunts will overcharge their Plasma Pistol, (albeit only in Reach and Halo 4) which will instantly deplete your shields. In Halo 4, they are much more dangerous when wielding Needlers, as the shards can now supercombine in players, killing them on any difficulty other than Easy. Grunts are especially dangerous in groups. Their combined fire, even with weaker Plasma Pistols, can quickly erode an enemy's shields. Grunts often operate Shade Turrets, which are very dangerous. Grunts are almost never seen equipped with two-handed weapons like Covenant Carbines, Brute Shots, Beam Rifles, etc. The exceptions to this are the Fuel Rod Gun and the Rocket Launcher (when given by the player in Halo 2) which are fired with two hands. Special Operations Grunts and Grunt Heavies are occasionally seen bearing these Fuel Rod Guns. Grunt Heavies can carry folded Plasma cannons. On The Storm and The Ark, a Grunt can be seen with a Brute Spiker. If a Grunt is in a Phantom that is shot down, and somehow manages to survive, it will sometimes be wielding a Spiker. Take note that a Grunt will not fire his Fuel Rod Gun if the enemy is too close to them, rendering them, for the moment, harmless.
All Grunts are equipped with and often use Plasma Grenades, although higher-ranking Grunts such as Ultra Grunts, Special Operations Grunts and Major Grunts throw grenades in combat more often. Special Operations Grunts also use Fuel Rod Guns in combat. Grunt squads in Halo 3: ODST seem to always have at least one grunt with a Fuel Rod Gun especially in Firefight. With the Catch skull enabled, Grunt Heavies have been observed throwing upwards of six plasma grenades. They have been known to "'Spam'" Plasma Grenades on the Legendary difficulty, which means that in a group of 10 Grunts, as many as eight of them will throw Plasma Grenades, one after the other, in an attempt to easily dispatch their foes.
In Halo 3, Halo: Reach and Halo 4 Grunts will arm two Plasma Grenades and rush to the player, causing an explosion as a result of being frightened or observing allies being killed. These Grunts are generally referred to as "Kamikaze Grunts." In Halo: Reach, if a Suicide Grunt(s) is running at you, and you use a jet pack, he or they will explode as soon as you get about 2 meters above them. In Halo Wars, Suicide Grunts are a special forces unit, starting with a Plasma Pistol, being only the leader-specific unit of the Arbiter. These Grunts have large, cylindrical methane tanks on their backs which hold far more of the gas than other Grunt's tanks. These tanks are used as explosives. The grunts charge at their enemies and detonate their methane bombs, causing massive splash damage. An example of this is the fact that at least 10 fully-upgraded Suicide Grunts can destroy a UNSC base. Suicide Grunts will also charge their plasma pistols, making them very effective against the Prophet of Regret, the Spartans, Wraiths and Ghosts with shields and Shield Generators.
In Halo Wars, the Grunt Squad serves as the main infantry unit for the Covenant Army, as goes with all games. On default, the squad is composed of three Unggoy commanded by either an Elite Minor, or a Brute Minor, depending on whichever individual was selected to be the leader unit for the game. They are the direct counterpart to the "Marine Squad" unit of the UNSC, serving as an all-round infantry unit. Though they may be inferior to "Marine Squads," they do move slightly faster. As with all Covenant units, the Grunt Squad is inferior to the Marine Squad, in both armament and skill. Being the main infantry unit, the Grunt Squad is effective against most types of units due to its varied armament. Their standard, primary weapon is the plasma pistol, and their secondary weapon/special ability is the plasma grenade, which is much more effective against light vehicles and even armor.
As with all Halo Wars units, the Grunt Squad can receive three upgrades to significantly increase their combat effectiveness. The upgrades are in order as follows:
- Peons - Upgrades the Squad with one additional grunt.
- Needler - Upgrades the Grunts with Needlers rather than Plasma Pistol, increasing their damage.
- Deacon - Adds a Grunt Deacon to the Squad. Deacons will sometimes outlive their Elite/Brute leader and the entire squad. They guide the squad with battle cries and promises of the Great Journey. A Deacon boosts combat values through spirituality. Note that the actual effect of the Deacon is a further increase in damage.
- "Zeal": Speed boost while in Suicide mode.
- "Defile": Suicide explosion does extra splash damage.