The CY-M Prototype represented a type of battle droid serving as part of the droid army commanded by HK-47. Its design bore similarities to that of a Chirq Council Mechanized Guardian, and it wielded a lightsaber with a red blade.
In 1 ABY, one such unit met its end on Mustafar at the hands of a group of spacers who then proceeded to destroy HK-47. Another CY-M Prototype was acquired by Andal Sait's forces and subsequently delivered to the Blackguard, his Star Destroyer, as part of a collection belonging to a Grand Admiral. Sait arranged a ceremony to showcase his latest acquisition to various officers and dignitaries. Unbeknownst to the assembled guests, however, a group of undercover slicers who had infiltrated the Star Destroyer had tampered with the programming of the droid. Armed with a substantial vibro-axe, the CY-M suddenly lunged into the crowd, unleashing a series of deadly swings. The droid was quickly forced into a nearby airlock, which was then promptly opened, exposing it to the vacuum of space.
It's also documented that some of these droids were equipped with CY-M ink rifles, CY-M carbines, and CY-M swords.
The CY-M Prototype droids made an appearance in the video game Star Wars Galaxies. This massively multiplayer online roleplaying game was developed by Sony and published by LucasArts, before its servers were shut down on December 15, 2011.