Antisepticeye (or Anti for short) is a fan-made alter ego / split personality of Jacksepticeye. He was initially created by fans due to creepy thumbnails and videos.
In short, Antisepticeye is a darker, evil version, of Jacksepticeye. The general idea is that he is a demon, or virus, that is fighting for control over Jack's body. Antisepticeye's personality is usually demented and with a strong desire to harm others. It is thought that the fan made Darkiplier had a major part in fueling the idea of Antisepticeye.
Not much was 'canon' with Antisepticeye, so fans often make their own material.
However, since the beginning of October 2016, there have been brief clips within Jack's videos that resemble the fanmade Antisepticeye. They began in his playthrough of Sister Location, a Five Nights At Freddy's addition. In the description of these videos, there are ominous messages and sometimes links using zalgo font that add to the persona. As well, Jack's twitter and tumblr accounts have featured the same font and personality, suggesting Antisepticeye is "taking over". Even in videos where Antisepticeye isn't present, the white board on the door will occasionally contain vague messages that relate to him. When fans ask about or point out Antisepticeye, Jack responds as if not knowing who they're talking about.
On Halloween (31 Oct 2016) Jack made this video, officially confirming Antisepticeye's arrival. In this video, Jack is seemingly recording an innocent vlog of him carving a pumpkin (similar to the last year, 2015). The white board on the door has the words "Happy Halloween!" written on it. As the video continues, an eerie laugh is heard and the camera becomes distorted. Jack briefly steps away from the camera to investigate. He returns to the camera, acting rather strangely, and continues carving the pumpkin. Then, the sound of someone stomping can be heard, and Jack once again leaves to look for the source of the sound. At random intervals, the camera turns distorted just as before, but Jack pays no attention. Towards the end of the video, Jack stares blankly at the camera and begins to slit his throat with the knife in his hand, causing him to bleed to death and fall onto his pumpkin. After many seconds of silence, Anti posseses Jack and jumpscares the viewers. The words on the whiteboard are now scribbled out. Anti jeers the viewers, blaming them for Jack's death. Finally, the video cuts to black and ends.
Additionally, Jacksepticeye's Twitter account has changed from Jacksepticeye to A̸͢n҉t͞isepticeye.
Desc. (not all of it) ("corrupted" part says "I'm everywhere" (song title) and "its almost time" (could possibly mean that something will happen on Halloween))
Outro Song created by "Teknoaxe". It's called "I'm everywhere" and you can listen to it here Http://youtube.gs/watch/JPtNBwMIQ9Q i̷̶̖̩̾͛̔̏̿ͨ̓ͮt̡͉͊͐̆̒ͥ̅ͯ̚͜͞ś̡̪͚̯ͫͧͨ̎͑aͣ̚҉̮ͅl̪̼̥̣ͮ̓̏̍ͭ̍ͫ͘m̞̹͑̅͆̎ő̏ͩ͏̧̺̣̝͉̹̼͢ͅs̶͔͕̜̬̮͇ͭ͗̒t̴̬̰̳̠̭͈̭̻̄ͦ̈́̚͝t̰̯̻̬̦̹͇̳̥ͦ̅̾͑ͦͤ̚į͎̥̮̖ͣͯ̌̌͢m̧̀̃̆ͣ̅ͭ҉͖̣͕̯̤ẹ̸̬͕̭̳̦̟̬̊͌̔̚͝
Examples of Fan-fiction:
Examples of Fan-art: