Mithos is introduced in Tales of Symphonia under his surname as an adult, but he is able to change into his child body since his appearance and growth are controlled by his Exsphere. He was originally a kind-hearted person despite the discrimination he faced for being a half-elf. Four thousand years prior to the game, he and his companions, Martel, Kratos Aurion, and Yuan, ended the war between the countries Sylvarant and Tethe'alla by using the Eternal Sword and splitting the two into different worlds. His plan was to reunite the worlds when the comet known as Derris Kharlan approaches Earth so he can use its mana to germinate the Great Seed into a Giant Kharlan Tree. The humans attempted to monopolize the Great Seed and killed Martel in the process. Daunted by her death, Mithos delayed the germination and instead placed Martel's soul inside the Great Seed until he could find a new body for her. Her death caused him to gain a strong hatred towards the world and become cruel and merciless. Years later, Mithos formed the organization known as Cruxis in order to find a compatible body for Martel and to fulfill his Age of Lifeless Beings plan, a plan where everyone's consciousness will live inside their Exspheres free from their body; the latter being a twisted interpretation of Martel's last wish, which was to end discrimination between all the different races. Mithos' ideas resulted in the deaths and suffering of many people and the party was forced to kill him.
In Super Smash Flash 2
Mithos Yggdrasill is the main hazard of the stageTower of Salvation in Super Smash Flash 2. He hovers around the top of the stage and occasionally attacks the players with one of three Light-elemental artes that he uses in Tales of Symphonia: Yggdrasill Laser (ユグドラシルレーザー), in which he fires a large horizontal laser between the two moving platforms that deals 14% damage to opponents hit; Holy Lance (ホーリーランス / ホーリィランス), in which he flies away and spears of light rain toward the platforms on the sides and deal 4% damage each; and Death Eater (ディースネル), in which he slams his fist into the ground at the center of the stage as four separate beams rain from the sky and deal 9% damage each. Players are also able to attack him, and when attacked, he counters with a punch forward that deals about 8% damage to opponents hit.
Lloyd attacking Mithos with Tempest while Mithos counterattacks.
Mithos hitting Link with Death Eater next to Marth.
Mithos preparing to use Yggdrasill Laser.
Mithos hitting Lloyd and Ichigo with Yggdrasill Laser.