Mad Jack, also called Quack in the Box, is the third boss of the game Donkey Kong 64. It is fought in Frantic Factory by Tiny Kong. Because of the battle style, Mad Jack is considered one of the hardest bosses in the game.
The battle takes place in a large area on top of some platforms each are either blue or white in color. Mad Jack will hop around in his box attempting to crush Tiny. After bouncing around enough, Mad Jack will pop out of his box and throw fireballs at Tiny. After getting hit enough times, he will turn invisible and shoot lasers instead.
Tiny must have learned the Pony Tail Twirl from Cranky Kong first in order to even have a chance in this battle. Tiny must fly around to avoid being crushed by Mad Jack's box. When Mad Jack pops out of his box, two switches will appear on either a white or blue platform. Tiny must Simian Slam the switch on the same colored platform as Mad Jack meaning if Mad Jack is on a blue platform, Tiny must press the switch on another blue platform. After Mad Jack turns invisible, he can still be spotted with the sparkles in the air. Tiny must also be careful of the lasers as Mad Jack tends to fire them ahead and the blast range takes up an entire platform making it unavoidable if Tiny is still on the targeted platform. After Tiny strikes Mad Jack five times, he will crash down below and the Boss Key will be Tiny's.
- Originally, Mad Jack was going to be called Junk in the Box and was going to be composed of junk.
- It is unknown if Mad Jack is working with King K. Rool or just protecting his territory. However, since Mad Jack has a Boss Key, it can be assumed he is.
- Mad Jack's laugh is similar to that of the Disney character Donald Duck.