The GLOM (Giant Likeness Outputting Machine) is a device featured in the Nintendo Adventure Book Double Trouble. Built over the course of several weeks by Iggy Koopa, the GLOM can make sand clones out of anything it sees, even through images broadcast by the spy camera flowers planted by Iggy throughout the Mushroom Kingdom. An intimidating machine, the GLOM is ten-feet tall, moves through a combination of wheels, tank treads and mechanical legs, and is covered in electronic eyes, telescoping arms, and miniature television sets, all of which are inexplicably showing old monster movies. When it moves, the machine leaves a trail of slime, presumably some form of waste created by the cloning process.
When Mario finds Iggy in his Fort Koopa laboratory in the Koopahari Desert, the Koopaling summons the GLOM to attack him. As the machine advances on him, flailing its arms, Mario can lure it to the hall of mirrors outside the room, where the GLOM will create a duplicate of itself after seeing its own reflection. The two GLOMs then make more GLOMs, and continue doing so until the original overloads and blows up, causing an explosion powerful enough to bring down Fort Koopa. With the GLOM gone, all the clones it created dissolve back into sand.
In two other possible scenarios, Mario is knocked out and dumped back in the hall of mirrors, either after fighting his own clone to the point of exhaustion, or after being swarmed by a group of Iggy clones.