Tested and confirmed working. This is a modified BOSS Blues Driver by Keely. A rare piece of equipment known for being used by John Mayer. As the name "Phat Mod" suggests (also playing on "FAT" for thick and good sound), turning the switch on boosts the bass significantly, resulting in a dense and very cool distortion sound. It also retains the core clean sound that the Blues Driver is known for, making it a very versatile pedal. Due to the small number of units and its high level of completion, few people sell them, making it a very valuable piece of equipment nowadays. I am also listing this on other sites, so please forgive me if it sells out. Please let me know your desired price in the comments section for price negotiations. (We receive many inquiries that are just for fun, so we are not using the "offer price" feature.)