From 1d4chan
It is like the Voynich Manuscript, nobody knows how this thing works and nobody knows how to use it effectively.

The Neuro-Disruptor is a weird, WEIRD weapon. Imagine a crystal that has been carved into a shape of a gun which resembles some Neckbeard's dollar store space gun that goes pew pew. Except these pew pew can cause erratic seizures and brain shutdowns. It functions similarly to the Neural Shredder but its mechanics are beyond alien. The Neuro-Disruptor is a psycho-crystalline weapon of unknown alien manufacture, used most commonly by the Eldar Harlequins. It is a handgun made of a transparent crystalline material, or more accurately someone stuck a rock onto an empty pistol frame and called it a day. Even the Orks would call this half-assed.

Upon closer examination, it is indeed literally a rock glued to a gun frame, as there are no power sources or mechanical parts within the gun, it's fired solely by the mind of the user. Its essentially a quasi-magic wand in the shape of a gun, meant more as a conduit for the user's abilities, if said ability was confined to them lobotomizing targets at will, so its like a magic wand with a pre-set spell inside.

It uses intricate psycho-crystalline circuitry to emit a wave of particles that disrupt the brain's neural pathways. Armour offers no protection from the Neuro-disruptor and only those of mental fortitude (Read: a battle-hardened Psyker) could resist the affects of the Neuro-Disruptor.

For its more spooky counterpart, see here:

Weapons of the Eldar
Ballistics: Shuriken Pistol - Harlequin's Embrace - Harlequin's Kiss
Directed-Energy: Fusion Pistol - Mandiblaster
Sonic: Banshee Mask
Warpcraft: Neuro-Disruptor
Other: Neural Shredder
Basic Weapons:
Ballistics: Avenger Shuriken Catapult - Death Spinner - Gatekeepers Bastion
Reaper Launcher - Shuriken Catapult - Shuriken Rifle
Swooping Hawk Grenade Pack
Directed-Energy: Cloudsweeper - Fusion Gun - Lasblaster
Laser Lance - Prism Rifle - Ranger Long Rifle
Incendiary: Eldar Flamer
Exarch Weapons:
Ballistics: Spinneret Rifle - Tempest Launcher
Directed-Energy: Fire Pike - Hawk's Talon - Prism Blaster - Star Lance - Sunrifle
Incendiary: Dragon's Breath Flamer
Heavy Weapons:
Ballistics: Eldar Missile Launcher - Pack Grenade Launcher - Mirage Launcher - Shadow Weaver
Shrieker Cannon - Shuriken Cannon - Torrent Reaper Launcher
Directed-Energy: Bright Lance - Scatter Laser - Starcannon
Haywire Cannon - Firestorm Scatter Laser
Sonic: Vibro Cannon
Warpcraft: Wraithcannon - D-Scythe
Vehicle Weapons:
Ballistics: Doom Weaver - Phoenix Missile Launcher
Directed-Energy: Prism Cannon - Pulse Laser - Prismatic Cannon
Warpcraft: D-Cannon - D-Flail
Super Heavy Weapons:
Ballistics: Deathshroud Cannon - Phantom Missile Launcher
Revenant Missile Launcher - Void Spinner Array
Directed-Energy: Inferno Lance - Pulsar - Suncannon
Sonic: Sonic Lance
Warpcraft: Psychic Lance
Ship Weapons:
Ballistics: Torpedo
Directed-Energy: Naval Lascannon - Phantom Lance - Pulsar Lance
Shadow Lance - Heavy Starcannon
Non-Firearm Weapons:
Melee Weapons: Eldar Chain Weapons - Eldar Power Weapons
Eldar Force Weapons - Miscellaneous Weapons
Grenades & Explosives Plasma Grenade - Haywire Grenade - Hallucinogen Grenade