Mad Jack is a killer Jack-In-The-Box created by King K. Rool and a supporting antagonist in Donkey Kong 64. He possess the ability to throw fireballs, shoot lasers and even turn invisible
In "War of the Villains", Brad purchased Mad Jack in an attempt to scare Sid Phillips. Mad Jack came up to Sid as a simple box, but then grew to a tremendous size. He then popped out and proceeded to terrorize Sid. He finished his job by simply waving Good-Bye.
Later on, Brad would later lead Mad Jack on an attack on Darla Dimple's Mansion. However, Darla had a few tricks up her sleeve, including a switch pulled by her bulter Max to electrcute and send Mad Jack falling to his doom.