Neuro-Disruptor
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: