This sketch fills the screen with ghosts! It uses the cos() function to make the ghosts go left and right, and it uses an array to hold previous values to make the tail.
Click here to view this code in the p5 editor.

This is part of p5 spooky sketches printout I made for CC Fest in 2019. That printout contains a bunch of Halloween-themed examples of drawing and image manipulation. Feel free to use it on your own or in a classroom!