Swartz's Army is an army of past enemies of the Kamen Riders assembled by the Time Jacker Swartz to assist him in his goal of merging the worlds together and major antagonists in the final arc of Kamen Rider Zi-O.
As Swartz's plans reached their final stages, the Skywall from the World of Build arose in Zi-O's timeline and from it past enemies of the Kamen Riders such as the Guardians and Roidmudes emerged to cause havoc. Soon after, the Futo City Tower and Yggdrasill Tower emerged as more enemies such as the Masquerade Dopants and Inves appeared, along with Mashin Chaser who, due to the shifting of the timelines, did not remember being Kamen Rider Protodrive and instead sought to destroy the Kamen Riders until Geiz reminded him of Gou Shijima.
After Sougo, Tsukuyomi, Tsukasa Kadoya and Daiki Kaitou returned from Tsukuyomi's timeline, they found themselves faced by Swartz's Army, which had grown even larger since their departure. As the army surrounded them and marched towards them, the Riders prepared for battle.
After the final confrontation between Swartz as Another Decade and Sougo Tokiwa as Oma Zi-O, the army that Swartz summoned disappeared once Swartz is dead.
- Mirror Monsters
- Bison Yummy
- Waste Yummies
- Gamma Commandos
- Kamen Rider Evol