Pentagon

A pentagon is an arctic blue piece of paper with 5 sides. It is apparently "extremely scary", according to Eraser.

Coverage
In Getting Teardrop to Talk, Pen shows Eraser what he believes is a rectangle. Eraser then corrects him by saying it's a parallelogram, and he would know (since he is a parallelogram, too). Pen then shows Eraser a pentagon, and Eraser is immediately terrified. Pen doesn't notice Eraser's fear and instead comments on how "Pentagon" is his name (Pen) if you added "-tagon" as a suffix. Eraser explains that pentagons are "extremely scary". Pen doesn't understand, until the pentagon intensifies causing both of them to scream. They call Blocky to fix the problem, who uses Saw to cut the pentagon into a (t')quadrilateral and a triangle. Pen comments on how he never wants to see a pentagon again.

Trivia

 * The pentagon has the ability to make the world around it darker, and the music playing more intense.
 * However, this could just be in Eraser and Pen's imagination, as Blocky and Saw seem to not notice this change. This could suggest that pentagons are not actually scary, but that Eraser and Pen have an irrational fear of them.
 * Its shape and color scheme are similar to Foldy, who appears in the next scene.
 * Pen and Eraser being scared of the Pentagon is related to the Pentagram which is seen as an sign of anarchism.