C'tan Phase Weapons
The Crons don't have that much in the Power Weapon armory (before 9e that is), but they don't need to when they have blades that can bypass all forms of armor to get deep into the juicy bits. This is where C'tan Phase Weapons come in.
A C'tan Phase Weapon (also known as a Fractal Edged Weapon), is based around a metal blade of unknown composition that, through the use of highly advanced Necron physics, is capable of phasing through any object irrespective of its physical properties. Energy shields, armor and even daemonic bodies are of no defense against a Phase Weapon. Due to its name, the C'tan Phase Weapon is both a rare and powerful tool of use. However, as a C'tan's raw substance is made of the same alloy and has the same properties, attacking a C'tan with a C'tan Phase Weapon disarms the attacker, as the metal becomes a part of the C'tan's body. In one instance, a Callidus Assassin attacked an Imperial Planetary Governor, only to have her C'tan Phase Weapon absorbed into the "governor" and become a part of his body. This Planetary Governor was most likely the C'tan shard called the Deceiver in another of its myriad disguises.
Despite its Xenos origin and questionable heretical nature, the Imperium of Man have taken a interests in these weapons. Whilst they don't know how this thing works, they do understand how useful it is to have a blade that ignores all types of armor, so they gave it to their best.
The most notable users of C'tan Phase Weapons are the elite Officio Assassinorum Assassins of the Callidus Temple in employ of the Imperial Inquisition. The Deathwatch utilize a similar weapon, known as a Xenophase Blade, an ancient and barely understood artifact weapon who some believe has its origins amongst long-defeated xenos dynasties, though speaking of its history has long been forbidden on pain of excruciation. Whether this type of weapon is one and the same, is not currently known.
C'tan Phase Blade
The most common Imperium Phase weapon is the blade found on those sexy, polymorphic ladies.
It is believed that the first Phase Blade was found on one of the long Dead Worlds of the C'tan. Excavations by the Adeptus Mechanicus uncovered numerous artifacts of extremely advanced technology, but of their makers, there was no evidence. Each individual phase blade utilized by a Callidus Assassin is optimized to reflect their user's favored combat stance and personal strengths, but they all take the form of an elongated punch-dagger. Their deadly blades are thought to utilize the lost xenos technology of the C'tan, though the Callidus Temple keeps their nature a close secret. The blade of the Phase Weapon is unusual in its ability to phase in and out of Realspace by molecular realignment, allowing it to plunge clean through armor, flesh and bone as though they were not there at all.
Unlike the C'tan Phase Blade, the Xenophase Blade is designed like a traditional single-bladed sword. Thus, there is very little need for practice when it comes to the utilization of these weapons.
Xenophase Blades are a type of weapon used by the Deathwatch. These weapons are ancient and barely understood artifacts. Xenos in origin, they ripple with a molecular realignment field that allows it to cleave through force fields and metaphysical wards easily. Speaking of the origins of these weapons is forbidden within the Deathwatch under penalty of excruciation and 'recycling'. It is unknown if it has the same problem of being absorbed by a C'Tan when used against them.
Whether this type of weapon is one and the same, is not currently known, although most in /tg/ says yes due to the blatantly Necron appearance. On tabletop, Xenophase blades are basically power swords that force a reroll on invuln saves, as they have the ability to teleport past armor. Needless to say, that makes them extremely invaluable weapons.
The most common type of Necron close combat weapon. A Warscythe is Necron weapon composed of Necrodermis and similar to the Phase Blades used by the Imperium. Warscythes are used by Necron Overlords, Necron Lords, Lychguards, and
Pariahs BLAM!. It is of a similar design to the Staff of Light, although it has no ranged attack (Didn't stop some Necrons from putting a Gauss Flayer on top of it) and is more formidable in combat. The Pariahs (When they still exist), however, carry a model of Warscythe that has a Gauss Blaster built into it. They are made of the same Living metal as their ships and bodies and can carry itself effortlessly through all types of armor, including heavy energy fields, thanks due to its own entropic field generator. A well directed attack can take off the end of a Leman Russ Battle Tank or scythe open the side of a bunker. A Warscythe's power core blazes with the heraldic color of its wielders Necron Dynasty.
A curious side effect of the warscythe’s power field is to render the weapon almost impossible to destroy. There are several well-documented instances of warscythes surviving direct hits from lascannons, and even from turbo-lasers, with little harm to show for it. Unfortunately, this protection does not extend to the wielder, and it is quite common for a warscythe to survive a battle where its master does not.