I'm barely awake, so I'll just throw the "Psychic Assault Statues" from the same issue out there...
Room 29. [You enter a large, square room, lit by 4 floating orbs that shine a brilliant green. On either side of the room there is a great procession of pillars which each have 8 faces. An opening in the far end of the chamber leads to a dark area of unknown size. Two 13-foot-tall iron statues stand to either side of the opening. Each looks somewhat humanoid, as it has 2 legs and carries a great sword in its two 3-fingered hands. However, the head of each statue much closer resembles that of a Mind Flayer, having 2 bulbous eyes separated by a bony ridge. Where a human mouth might be, the sculpture’s face forms into 8 long cilliated tentacles.
If the adventurers do not come within 25 feet of the statues, the structures will remain inanimate. In this condition, the figures will not be detected as evil, alive, or even magical. However, if someone does come within the prescribed radius, the 2 statues will suddenly and without warning come to life and attack. Each of the metallic creatures has 10 hit dice (80 hit points), armor class -6, movement 6”. Before engaging their enemies physically, the living statues will first use their psychic blasts. Each blast of mental energy will affect a conical area 40 feet long and 25 feet wide directly in front of the statue. It will inflict 7-42 points damage to all within the area. In addition, alI affected must make their saving throw or pass out for 10 melee rounds due to the psychic assault. If a victim makes his saving throw, he will take half damage and have all his psionic abilities disabled for 1-10 turns. The Guardians can do this only once. After blasting their opponents, the animated constructs will engage their opponents with their long, bizarre swords. Each of the oddly shaped weapons will strike at +5, and if successful, will inflict 4-40 points damage with its serrated edge. The attack can hit up to 4 opponents in a single swing if they are all within 15 feet of the statue. Each of the statues is immune to fire. Lightning and acid add to their hit points in a 1:1 ratio. They are 40% magic resistant and cannot be hit by weapons of less than +2 in enchantment.
The glowing orbs may be retrieved and each will glow with the light of a full moon for the next 10,000 years.
Originally appeared in Dragon Magazine #46 (1981).
I'm thinking it's a sword-version of a BFG, hence "BFS".
If we make it an exotic weapon with a higher reach it opens up a can of worm regarding PCs getting their hands on it, so I'd much rather make it something intrinsic to the creature. Either give it a "sword" attack that's actually a special weapon attack (or attacks) that's intrinsic to its body, have it possess an extended Reach, or simply make it a Huge creature so it has a natural 15 ft. reach.