Skull Kid's Forces are an army that serves Skull Kid, or so it seems at first glance. In reality, they serve the evil Majora, the embodiment of Majora's Mask. During the Era of the Hero of Time in the Child Timeline, Skull Kid's Forces threatened to destroy the parallel world of Termina.
Skull Kid's Forces presumably came into existence shortly after the mischievous Skull Kid stole Majora's Mask from the Happy Mask Salesman. Using the masks dark power, Skull Kid causes all sorts of problems in Termina. Though they started off as seemingly minion pranks, as Skull Kid was consumed further by the power of the mask, they became more dangerous, leading to lethal consequences for the Deku Butler's Son, Darmani, and Mikau. However fortunately, Skull Kid made the mistake of stealing the horse and Ocarina of the young Hero of Time, who had been sent back in time to relive his stolen childhood following the defeat of Ganondorf. Chasing after Skull Kid, the Hero of Time was transported to the land of Termina. Possibly sensing him as a potential threat, Majora used its power to transform the Hero into a Deku Scrub, presumably using the life force of the Deku Butler's son to do so, resulting in the young Deku Scrub's death. However one of Skull Kid's fairy companions, Tatl was left behind while she was fighting with Deku Link, causing her to reluctantly join forces with Deku Link in order to reunite with her brother Tael. However both found that Termina was been threatened with destruction by the Moon, which seemed to be under Skull Kid's control and were asked by the Happy Mask Salesman to retrieve an item that was stolen from him by Skull Kid. After regaining his Ocarina of Time, Deku Link used the Song of Time to rewind time back to the first day he arrived in Termina. After learning the Song of Healing, Deku Link was restored to his Hylian form and his cursed Deku form was sealed into the Deku Mask. After learning how dangerous Majora's Mask was, Link and Tatl journeyed to the Swamp of Woodfall, to find the ones who are there spoken of by Tael. They eventually discovered the ones Tael spoke of where the Four Giants, who had been friends with Skull Kid in the past. Using the powers and abilities of various masks, the Hero of Time defeated Odolwa, Goht, Gyorg, and Twinmold freeing the four giants. Returning to the Clock Tower on the Final Day, the Hero of Time summoned the four giants, who stopped the Moon from hitting Termina, causing Majora's hold on Skull Kid to weaken. However despite losing his host, Majora continued his mad plan to destroy Termina, forcing the Hero of Time and Tatl to confront Majora on the Moon. After trading all the masks he had acquired in Termina to the Lunar Children that inhabited the Moon, he received the power of Fierce Deity's Mask from the Lunar Child wearing Majora's Mask before being transported to a room where he engaged and defeated Majora.