Frieza, Cell, and many other villains in Hell wanted revenge against the Z-Fighters for killing them, and sought a way to strike back at them. Dr. Gero devised a plan, and created a small dimensional rift generator, and several special devices, which he handed to Frieza and Cell. After giving them instructions, Frieza and Cell were able to jump through a brief dimensional rift to Earth , and sought out Majuub. Upon ambushing Majuub, Cell used the first device Gero had given them, which had the effect of temporarily regressing Majuub back into Kid Buu.
After explaining to Buu the plan, the three villains proceeded to don a set of the other devices Gero provided them, the Fusion Necklaces. Once all three had been placed around their necks, they were joined together and formed the maniacal Maceza.
Attack on the Z-Fighters
Upon their fusion, Maceza immediately sought out the Saiyans who had given him the most trouble: Goku and Gohan. The two Saiyans valiantly fought against Maceza, but were fighting a losing battle. Meanwhile, having caught wind of Cell's alleged reappearance after someone had spotted him as he and Frieza were locating Majuub, Hercule arrived on the scene to investigate, and promptly hid like a coward. Not long after that, the Supreme Kais because aware of the disturbance in Hell, and Kibito Kai used Instantaneous Movement to travel to the Saiyans locations to give them a hand. He handed Goku some Potara Earrings, hoping they would fuse, and then quickly left. However, Maceza caught on and quickly knocked out Gohan. Frustrated, Goku continued fighting a losing battle against Maceza, until he was thrown into Hercule's hiding location.
After a brief explanation of the situation to Hercule, Hercule offered to be the one to fuse with Goku in place of Gohan. After a moment's thought, Goku reluctantly agreed, and the two merged into Gokule. Gokule then proceeded to square off against Maceza, fighting an even battle, lasting for several hours with neither side gaining an advantage.
Eventually, Vegeta and Future Trunks, having noticed the large power levels due to being nearby, came to investigate. Gokule told them that he was doing fine by himself, but he wouldn't mind if they helped, and thus they jumped into the fray. The tie began fading, with Maceza moving closer and closer to defeat. Eventually, Maceza decided enough was enough.
Maceza revealed that Dr. Gero had given him one other device, a device which could release the hidden potential in a being. He proceeded to use it on himself, and tranformed into Perfect Maceza. He then began to regain his advantage, first beating down Future Trunks, then Vegeta, then Gokule. Gokule offered his Potara Earrings to the two, saying that it might turn the tide in their favor. Although Vegeta initially refused, Future Trunks and Gokule were eventually able to convince him, and the two merged into Vegetunks. Vegetunks, alongside Gokule, were enough to destroy the Fusion Necklace that Maceza was wearing, causing him to separate back into Freiza, Cell, and Majuub. Majuub, Gokule and Vegetunks then vaporized Frieza and Cell. Since the two were already dead, they were erased from existence, thus meaning that Maceza would never appear again.