Why did Slig masks change?
Following a high rate of Slig suicides, an investigation into that particular issue of masks revealed that the visors in them contained a small optical misalignment, effectively giving the poor wearers double vision. The next generation of visor technology was quickly issued to prevent more cross-eyed deaths. Note that higher ranks of Sligs, such as Magnums and Big Whammies, have a different visor design yet, no doubt increasing their visual acuity. From a design perspective, OWI felt that they needed to create more emotion from Industrial characters, and that two separate eyes would give Sligs a more expressional face.
