A B1 battle droid, part of the Geonosian droid army, was present in the Petranaki Arena during the First Battle of Geonosis. This particular battle droid ended up with the head of C-3PO attached to its body after the protocol droid became entangled in the droid factory's conveyor system. Simultaneously, C-3PO's head was attached to the body of a B1 battle droid.
As the conflict unfolded, both the B1 droid and C-3PO found themselves fighting against several Jedi. The B1 droid commented on its reduced speed compared to other B1 units, attributing it to a potential maintenance problem. Subsequently, the droid targeted a solitary human Jedi, who skillfully redirected the blaster bolts back at the droid, causing it to lose its head. After the fight concluded, R2-D2 reconnected C-3PO's head to its original body.
Matthew Wood provided the voice for this unnamed battle droid in the 2002 [prequel trilogy] film, Star Wars: Episode II Attack of the Clones.