The B1 Assassin Droid was a special droid unit used by the CIS during the Clone Wars. They were programmed almost exactly the same as a IG-series assassin droid and always used sniper rifle to blast down clone troopers from afar.
The B1 Battle Droid Sniper was an basic B1battle droid unit that had special programming which allowed them to be able to give them better accuracy to help with their aim. Some early units of B1 assassin droid were colored red. As the war progressed, several veteran B1 Assassins had several scratches and blaster marks all over their bodies from the years of warfare they endured.
The B1 assassin droid was a variation of the B1 battle droid used by the Trade Federation and the Confederacy of Independent Systems over the course of the the Clone Wars. Their gyroscopic stabilizers and detailed target-selection programs made them very effective snipers, which proved lethal to the Galactic Republic's clone troopers. They were not, however, as common as the regular B1 battle droids, because it was costly to make a droid as accurate as an organic sniper could be. During the Clone Wars, battle droid assassins were deployed at the Battle of Geonosis in defense of the most important units waiting to be loaded onto transports and at the Battle of Muunilinst against Advanced Recon Commandos. Battle droid assassins were also used during the Battle of Tirahnn, and appeared on a number of battlefronts throughout the Clone Wars. Following the end of the conflict and the shutdown of the Separatist Droid Army, battle droids were reactivated and used by the rogue Geonosian Gizor Dellso in his army up until the Battle of Mustafar.