The Halo universe is a robust one, filled with different races, fantastic technology, and powerful weaponry in a time plagued with constant war. The weapons of Halo vary in power and scale throughout the series, but sometimes they don't feel as strong as they should in the hands of the player.
The disconnect between weapon strength in-game and their power levels in the lore can create some confusing cases for players, where a weapon can be less interesting or underwhelming. Halo's weaponry also goes beyond the guns and melee weapons showcased in the games, so weaponry from other Halo sources will be mentioned as well.
NOVA Bomb
The NOVA Bomb is a weapon capable of tearing an entire planet apart. It's easily one of the most powerful weapons mentioned in the Halo franchise based on its power scale alone. The bomb itself is essentially multiple nuclear bombs put together in a casing. When the bombs go off, the casing turns the blast upon itself, multiplying its power hundreds of times.
After a NOVA bomb was set off between a planet and its moon, the damage recorded was immense. Over half the planet's surface was scorched, the moon was shattered, and any ships around the area were vaporized. The surface was flooded with radiation from the blast which killed everything living on the planet.
Halos
Halo Arrays are the most frightening weapon in all of the Halo universe because their purpose isn't to destroy or vaporize. The purpose of a Halo Array is simply to kill. Using radiation and frequency tuning, Halo Arrays are capable of destroying the nervous system of anything that has one. This is unlike any weapons in the modern world, or in the Halo franchise because there're no huge explosions or burns from plasma.
The biggest reason these weapons are so scary is their range. Halo Arrays can take out entire galaxies with ranges up to 50,000 light-years. Victims have no chance of escaping their blast radius because they travel much faster than the speed of light as well.
Glassing Beams
Glassing, also known as plasma bombardment, is a process used to make a planet uninhabitable. Reasons vary for using this, but the primary cause would be to control the spread of the Flood. Glassing beams are essentially large plasma cannons used to raze the surface of a planet beyond recognition.
These cannons are only wielded by large ships that intersect orbits around a planet consistently firing down at it. These weapons are extremely powerful and can even be used at low altitudes during battle. There're restrictions that prevent the use of glassing beams though, so they're not used too often.
Infinity's Super MAC
A Super MAC is a large cannon that fires metallic projectiles with the power of advanced magnets. These magnets propel the projectile through a cannon until it reaches almost half the speed of light, and fire it with pinpoint accuracy at its target. These weapons can shatter other ships into millions of fragments without much of a downside.
The MAC on the UNSC's ship, Infinity, is the most powerful of these weapons. In battle, it has shown to be almost unparalleled by any shielding system or armor from invading forces.
Forerunner Guardians
Guardians were created by the Forerunners to maintain order and police solar systems. To enforce this, they were also equipped with many powerful weapons. The weapons themselves are not made to devastate. Instead, they're made to stop whatever force the Forerunners didn't agree with. This means they could disrupt power to weapons and machinery, destroy infrastructure, and shoot antimatter to discourage enemies from running away.
The Guardians were massive machines, with a height of over 4,000 feet, and a mass of two hundred million tons. Their destructive power wasn't what made them so strong, it was the fear and awe they could cause in their targets, preventing wars and violence from even happening in the first place.
Fuel Rod Cannon
These cannons are mainly used for anti-vehicle purposes, taking down airships and ground-based vehicles. They fire highly energized and radioactive material, encased in shells, that explode on impact. The cannons themselves are also able to track the heat signatures of their targets, making it difficult to avoid a head-on attack from one of these weapons.
These weapons are usually found on Covenant vehicles like Banshees and Wraiths, making them deadly in combat. Depending on the vehicle, there might be more than one cannon to worry about and when they're extra mobile, it can be an enemy's worst nightmare.
SPNKR
This weapon is like a rocket launcher on steroids with a bunch of features for optimal warfare. The rockets are able to fly for long distances and can track their targets like vehicles and airships. What's so powerful about these rockets is their ability to spread damage over a wide area of effect. This enables the wielder to take out vehicles and tanks, along with the crew inside.
These weapons can be weaker in instances where infantry is involved because their area of effect is so big, it'll probably affect allied soldiers. On top of this, the reload process is long and difficult, so they're not meant for the heat of battle.
Void's Tear
The plasma pistols of Halo are underrated in the power they actually wield. Being able to shoot plasma from a pistol-sized weapon at a high rate of fire would be devastating in real life, killing anything in one hit. In Halo lore, these weapons are highly effective against most kinds of armor and are dreaded on the battlefield. Even if they don't kill their target, the impact from the magnetic field and the burns from the plasma will incapacitate anyone.
Void's Tear is an advanced version of this capable of drawing enemies into its blast before releasing the magnetic field around the plasma. This weapon is so powerful that it can topple vehicles and stop tanks in their tracks.
The Prophet's Bane
The Prophet's Bane is an advanced version of an energy sword. As a close-range weapon, it doesn't get much scarier than this. The sword is capable of piercing almost any soldier's armor up close, as well as dealing fatal blows with ease. The ionized particles that give the sword its energy immediately cauterize any wound they cause.
This particular sword is a weapon of legend that, when wielded in the right hands, has devastating possibilities unrivaled by any other close-quarters weapon. It certainly doesn't have the advantages of range and precision that other weapons in the Halo series do, but when it's in your face, you'd better run.
Nornfang
Nornfang is a custom SRS99-S5 AM sniper rifle with added benefits. These rifles have the unmatched range for weapons of their size, as well as ridiculous firepower. The rounds aren't armor piercing usually, but the stopping power will put anything on its rear end. Nornfang's electronic scope gives it an advantage over other snipers, with pinpoint accuracy.
This sniper rifle's power is not limited to long-range battles like its peers either. In the right hands, Nornfang can be wielded to take out enemies at close range due to it's lighter than average weight and recoil control. The downside to this is it can only hold 4 rounds, so its user must be frugal when firing.