Antisepticeye, also known as Anti

Anti was originally thought of by the fans, after seeing Darkiplier, Markiplier's dark alter ego. Dark acted as an inspiration for Antisepticeye and before long the fans came up with the ego. Anti grew in popularity with the fans and Sean soon took notice. 

Sean then began to work with the character and then made it his own. And thus, Antisepticeye as a character and an alter ego was born.

—Originally appeared on October 10, 2016

—His first appearance was in a Five Nights At Freddie's: Sister Location video on Sean's channel

—Anti is a virus/demon and often fights for control over Sean/power

—In the video where he first appears, Anti shows up in glitched clips in the video, and even left hints of his appearance in the title and in the description; the camera may also suffer from static

—Anti often leaves hints that he will appear in videos in the title or description of the same video

—When Anti appears in videos, it's also foreshadowed by Sean not feeling well and leaving the camera frame

—Sean, when Anti will appear, will suffer from eye/neck twitches and stare at the camera for several seconds

Antisepticeye is a tumultuous ego; often his moods shift very quickly. As an example, Anti can go from insane to angry to serious in a matter of seconds. Because of this, he is unpredictable and, combined with his anger and general disdain for others, extremely dangerous.

Anti is known to be demented and hateful, having an intense desire to cause harm to others. The harm is usually physical and he gets an immense amount of pleasure from enacting violence on others. 

When possessing Sean, Anti will often take jibes at Sean and harm his body in some way, and as stated before, takes pleasure in it. In other cases, the virus/demon will also mock/threaten the viewer, or even the other alter egos. Anti doesn't fear anyone or anything and for the most part seems to just be an entity of violence and hate and insanity.

Antisepticeye, in Anti fashion, has an awareness of Sean's other alter egos and harbors a deep hatred for all of them. Anti seems to think of Sean as his and considers him to be his "puppet." As well as possessing Sean, Anti can possess the other egos, and calls them puppets. He also resents them because they help Sean and like him, which is why he's developed a sort of hatred for the other egos.

Extremely so!

Whatever you do, stay away from Antisepticeye! He has shown himself to be violent and will inflict harm on whoever he needs—or wants—to, and he will not let anything or anyone get in the way of his goals.

When Dr. Schneeplestein, another one of Sean's egos, tried to heal Sean when the YouTuber was feeling unwell, Anti possessed Schneeplestein and prevented him from helping Sean. In another case, Anti possessed Jameson Jackson—a different ego—he used the knife Jackson was holding to threaten those watching at home. 

Anti has also attacked Chase Brody, yet another ego, and Brody's children in an act of rage.

He can and will murder or maim whoever he needs to in order to get to Sean and use him how he pleases. If he sees you as disposable, he will get rid of you.

Stay away from him at all costs!