From the Super Mario Wiki
The Blast-o-Matic is a powerful weapon King K. Rool attempts to use to destroy Donkey Kong Island during the events of Donkey Kong 64. It was designed by the weasel technician Snide, who is deprived of the weapon's blueprints and his membership in the Kremling Krew by K. Rool before the game begins. Sometime later, the Blast-o-Matic is incorporated into Crocodile Isle, K. Rool's mobile base of operations, but is damaged when Crocodile Isle collides with a rock near the island. To buy time to repair the weapon, K. Rool imprisons Diddy Kong, Lanky Kong, Tiny Kong, and Chunky Kong and confiscates Donkey Kong's Golden Banana hoard. While this works as intended, the Blast-o-Matic is eventually disabled through the Kongs' efforts in Hideout Helm.
Failure to shut down the Blast-o-Matic (or selecting the "Quit Game" option from the pause menu) results in a cinematic of K. Rool laughing as the Blast-o-Matic prepares to fire at Donkey Kong Island.