Creepers is a way to disguise your pressures. The way Coach Brian Nix, Head Coach at Alcoa High School in Tennessee, runs creepers is when they show the presentation of four known rushers. One of those players drops into coverage, and they bring a non-declared rusher.
The video below shows a portion of Coach Nick's Nix's Creepers Part 1 on Glazier Drive. His entire coaching system is available on Drive.
A big part of their pass rush system, when they get into known passing downs, is getting in the overfront and working line games.
They also use simulated pressures. The difference between those in the Alcoa terminology is in simulated pressures, they will show 5 or 6 rushers. They will drop some of those rushers into coverage, and bring an additional rusher.
If you have a good defensive end, the offense may adjust to offset with slide. lock protection. Alcoa wants to slide to that defensive end because he is a matchup problem which allows their creepers to become effective.
They have creepers that they feel are good against both run and pass. He believes in high school if you can call creepers or pressures on mixed downs, it helps you when your base defense is not working.