OO12345 first appeared in MM54321's Fury Of CandyCao7 Blooper, then antagonized OiramOiram12345 and the Shadowreavers where he gathered a legion of dopplegangers and villains to take over the castle. His most notable appearance was in OiramOiram12345 and the Dark Star X a.k.a The First Doppleganger War. He was DSX's most loyal and trusted servant as well as general of all DSX Dopplegangers. He attacked MM54321 and Lilyncookies (MM's friend), but was defeated. Later when the Youtubers reached Hell by breaking Oiram's Hell Lock, OO12345 and EI2 once again fought MM54321 and LG2 and lost yet again. But because when Mario and Luigi were fighting DSX it was absorbing their power and grew mighty powerful, it became powerful enough to destroy the Mushroom Kingdom and revert it to the Dopplegangers' Lair. There OO12345 and the other DSX Dopplegangers revealed their true forms: A demonic deformed body with black angry eyes and red pupils. OO12345 realized the war was going to go on again and again because there a opposite of DSX, called the Light Star X, that was reviving heroes while DSX was reviving dopplegangers. OO12345 went crazy and decided to merge the DSX and LSX together, because a saying said if light and dark merge together both shall be destroyed, and since LSX and DSX were in charge of all beings if they died, all of their subjects would become null. OO12345 eventually succeeded DSX to be in charge of the evil star, but found a better plan to merge himself, DSX, Dark Bowser (Bowser's evil clone), Bowser X (Bowser's X form), and the combined power of all DSX dopplegangers to create the ultimate X boss creature: Dark Bowser X!!! Mario fights and defeats DBX, so OO12345 uses the DSX to combine and battle MM54321 in his X form, OiramOiram12345 X. MM54321 also combines with the LSX to become MarioMario54321 X, and fights the final battle with OO12345 X. OO12345 X loses and the DSX declares all DSX Dopplegangers all permanently null, so they all perish and reside and Dimension X. His friend Ztarman3 carries on his legacy by starting the Second Doppleganger War (Starman3's Blooper 40). In MarioMario761's Super Mario: Next Generation, a non-canon timeline to MM54321's videos is revealed: The Dark Star X didn't null the dopplegangers, he sent them to an area called Planet Dopple, but the Purple ??? and the Green ??? (Main antagonists of SMNG) infect all of them so OO12345 wants revenge. He goes to the castle but gets infected.
OO12345 has a sense of vengeance and has a strong hatred towards LSX counterparts. He is cruel hearted and mean and is one of the three Super Dopple Guardians picked by Xyther himself, the other two being Ztarman3 and SuperMarioGlitchy3.