Myson

Myson makes an appearance in Yuri and Constance's shared paralogue, A Cursed Relic, where he performed several experiments in secret. Learning that a Relic had been acquired by Duke Gerth, he led a group of Agarthans to steal the Relic, and used the results of his experiment to forcefully control a group of thieves. One of these thieves attempted to attack Gerth, only to be killed and revived as a Demonic Beast. He was surprised by the appearance of Byleth and their students, considering them an "unexpected obstacle", but was greatly pleased by the results of his experiments.

Despite the assistance of the Demonic Beasts, Myson was defeated by Byleth and their students. He expressed disappointment in not being able to obtain the Hero's Relic, but was content enough with the results of his experiments and withdrew. The Relic that he had intended to steal were the Fetters of Dromi.

Myson, alongside other high-ranking members of Those Who Slither in the Dark, appear during the battle at Shambhala against the Resistance Army/Alliance army, where he may be slain or simply ignored. Unlike the rest of the named soldiers, Myson's death will not affect the rest of the battle in any way.

Myson appears in the final battle against the Imperial and Kingdom forces at the Enbarr palace. Prior to the battle, Ingrid (or Gilbert if Ingrid was not deployed) notices that several of the Imperial mages weren't wearing their typical uniforms. If Myson is killed, the remaining agents will retreat from the palace, unwilling to sacrifice their goal attempting to defend Edelgard.