In Mother 3.5, PROJECT DARKDRAGON is one of the major plot points, leading up to the climactic scene. It was the ultimate weapon of the Three-Mile Army before their untimely destruction at the hands of some unnamed enemy army. They never got the chance to unleash PROJECT DARKDRAGON during their time. However, it was kept intact thanks to the Seven Needles. Porky Minch learned about PROJECT DARKDRAGON, having travelled to every time in the past and made it his mission during his time in the Nowhere Islands to see the project through to its end.
PROJECT DARKDRAGON is the world's most powerful bomb, with the force to obliterate the entire planet. However, it remains inactive until at least four of the seven switches keeping it dormant are activated.
It gets its name from the mysterious Dark Dragon of Mother 3, said to be "the power of the Earth itself." The difference between the two is that no matter who activates the switches, the PROJECT DARKDRAGON will always cause destruction.
Unless of course, there was some way to pull the switches out without agitating the bomb.