Jim Dunlop MXR Custom Badass Modified Overdrive Pedal by MXR (M77)
MXR M77 Custom Badass Overdrive « Guitar Effect
The MXR classic overdrive pedal has a hidden switch inside that changes to the Zakk Wylde overdrive. I've seen people mod their own switch for it, but I just drilled a hole
MXR Classic Overdrive - Flip a Switch to Make It a Zakk Wylde ZW44! : 5 Steps - Instructables