When designing the characters in Monsters vs. Robots, I wanted all the robots to look like they were created by a single inventor. In addition to giving them the same color palette, I tried to create a family resemblance between the robots by giving each of them the same style of eyes and antenna. This gives them a unified look, even if the rest of their body shapes diverge.

I did the same thing for all the monster characters, who all share similar horns and eyes.

Additionally, I wanted the robots and monsters to share some characteristics, both as a way to add cohesiveness to the illustrations, as well as to show that in the end they’re not so different from one another. So I made their eyes all the same light yellow color. And while all the robots have antenna coming out their heads, the monsters all have corresponding horns.