They are big humanoid robots with a muscular body, similar to an adult male human. They have no facial features, except they have 2 dents in the place where eyes would normally be (similar to Slenderman).
A Perplexahedron Guard first appeared when Ben Tennyson as Humungusaur touched it, when it was disguised as a wall and it punched Humungusaur. Kevin Levin attacked it and then Hunungusaur ripped it apart.
Another Perplexahedron guard attacked Gwen Tennyson. Gwen destroyed the robot.
A third guard's head was severed by Kevin. Another one was satbbed by Kevin, causing it to melt whilst the last one was destroyed by Gwen.
Due to the Perplexahedron being destroyed, all of the guards are destroyed.