The Blast-O-Matic machine is a laser device with three brass rings surrounding a metal arrowhead pole. This pole retracts into the belly of K. Rool's ship, and is powered by a massive computer in the heart of the ship that draws energy from five Banana Medals.
After his defeat in the events of Donkey Kong Country 3: Dixie Kong's Double Trouble! and Donkey Kong Land 3, King K. Rool plotted to destroy DK Island in retaliation. In the now mechanized Crocodile Isle, which has been turned into a ship in K. Rool's image, he had all possible members of the Kremling Krew work on building the machine, with Snide heading the development. After most of the design is finished, K. Rool becomes paranoid in regards to Snide, and fires him, breaking up the Blueprints of the device and giving them to his Kasplats for safe keeping.
As the machine's development nears completion, Crocodile Isle sets off for DK Island, and though the ship crashes and seemingly loses its mobility, it finds itself positioned perfectly before DK Island. With the machine still unfinished, K. Rool sends his henchmen to steal Donkey Kong's Golden Banana hoard and kidnap his friends, Diddy (after he challenged and fought the entire Kremling Krew on his own), Lanky, Tiny, and Chunky, scheming to distract him with getting them all back while focusing on finishing the Blast-O-Matic machine.
While he makes every attempt to stop them from succeeding, including sending out his elite henchmen Army Dillo and Dogadon, the Kongs make unexpected progress in recovering what was lost to them, to the point where K. Rool begins to feel apprehension about it by the time they reach Gloomy Galleon. He consults his chief of staff to ask about the progress on the machine, and the nervous Kremling replies that they weren't ready yet, blaming it on his men, who blame him in turn. K. Rool sends Klaptraps to supervise the machine's construction.
K. Rool later learns that by the guidance of a vengeful Snide, the Kongs have been recovering the blueprints to the Blast-O-Matic from his Kasplats. One Kasplat, realizing the danger of the situation, attempts to flee before K. Rool can inflict repercussions...only to find himself face-to-face with a giant red Klaptrap that K. Rool used to execute him.
The Kongs eventually succeed in reaching Hideout Helm, and a frenzied K. Rool orders his men to activate the machine, despite the risks of it blowing up on them. Unfortunately, thanks to the recovered blueprints, Snide manages to buy the Kongs enough time to reach the supercomputer powering the laser, fight through all of the defense systems, and take the Banana Medal power cores, shutting the machine down for good.
If you choose to quit the game or if you fail to deactivate the Blast-O-Matic within the allotted amount of time, you incur the game over scene which shows the Blast-O-Matic activated and pointing at DK Isle, just before destroying it.
In order to deactivate the machine and save DK Island (before the Kremlings repair it), the Kongs must collect Blueprints from Kasplats during their adventure, give them to Snide, and then enter Hideout Helm. Depending on how many Blueprints the Kongs collect, the Blast-O-Matic will be delayed from destroying DK Island; the default amount of time is ten minutes, with an additional minute granted for each Blueprint turned in to Snide, making the maximum amount of time 50 minutes.
Upon reaching the power core in Hideout Helm, the player will find a Gorilla Grab switch. Pulling it will cause 5 DK stars to appear around the power core. Diddy will have to use the nearby Rocketbarrel to fly through all of the stars in 60 seconds. Success will open the steel doors that lead to the generator rooms. Four of these are also barricaded with fences that Chunky will need to Primate Punch. After that, Donkey Kong can approach the first chamber, which is unlocked by Bongo Blast. Within, he'll find two challenge barrels of K. Rool's design; clearing both of them will deactivate the first power stream, upon which Donkey Kong can claim the Banana Medal that fueled the machine. The process must then be repeated with each of the Kongs in turn at their own respective doors, with Chunky, Lanky, Tiny, and Diddy, who will need the Rocketbarrel to reach his chamber. If Diddy clears the last challenge barrel before the countdown runs out, the machine will be permanently shut down.
- It is unknown as to how the Kongs can increase their time to deactivate the Blast-O-Matic by returning blueprints when Snide has no access to the weapon.
- If the player fails to claim the Banana Medals that powered the Blast-O-Matic before leaving Hideout Helm, they will be lost forever.
- In the later game Banjo-Tooie, there is a similar device by a similar name called the Big-O-Blaster, commonly referred to as "BOB", which was used by Gruntilda to drain life force.
- The Blast-O-Matic reappears in Super Smash Bros. Ultimate as King K. Rool's final smash. K. Rool cackles in his throne room as he triggers the machine, successfully firing the laser and eradicating DK Island.