He came from an AU called "X-Tale".
He was created by Tumblr user Jakei95.
Cross usually has one white pupil and one red pupil, and a red lightning bolt shaped "scar" under his right eye socket. This is a signal how Chara is there. His eyes can change like most sans' eyes (totally black, all white). Just like how he can have totally white eyes, he can also have completely red eyes. Completely red eyes signal when he is feeling strong Chara-like emotions. His soul is half an upside-down white monster soul and half a red human soul. He is only alive because chara "paired up" with him using his half determination to keep him alive.
He wears mostly black and white. His attire consists of a black jacket with a hood and several white attachments and white fluff on the hood, black shorts with white Xs on each leg and white shoes with Xs on them. He wears a gold locket and a black and white tattered scarf. His main weapon is a giant knife.
NOTE: Chara is not a girl, rather an 18-year-old boy in a 10-year-old's body. This has been confirmed by Cross' creator (Jakei).
Cross could take control of a victim by executing them temporarily to make the victim their puppet. Cross can also steal parts of universes with his blade.
Stolen Abilities Edit
Cross and Chara stole half of Sans' soul, which enables them to have Classic Sans' abilities. Cross has a Gaster Blaster that has four eyes and red pupils that fires red laser beams instead of blue. He can use a knife like a weapon instead of bones. The knife ability most likely came from Chara and his determination.
Cross lived in a universe called X-tale, somewhat like Sans. He had friends and family. His Gaster and ink sans destroyed his world to make a better one and and she (chara) was somehow trapped within Cross's soul. His world had no resets or true resets so he stayed in that state for a long while. He has a plan to get his world back, to steal from other AUs and use their code to make his (this is Underverse). His world is currently a white space.