Pencil is a tool in OE-Cake that is unique in that it draws a perfect line of continuous particles in series, spaced standardDistance apart, making smooth slopes easy. In comparison, the Brush tool draws on a grid which leads to rougher surfaces and difficulty drawing particularly thin lines.

Pencil can non-destructively draw on currently existing Rigid objects. If you make your first particle closer than standardDistance from a particle on the Rigid object, but make sure no particles are overwritten, anything you draw will be part of that Rigid object.