Antisepticeye (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 fueled the idea of Antisepticeye.
Not much is '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 Antisepticeye. They began in his playthrough of Five Nights At Freddy's Sister Location. 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.
Additionally, Jack's Twitter account has changed from Jacksepticeye to A̸͢n҉t͞isepticeye.
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. At one point in the video Jack's nose starts to bleed; he briefly steps away from the camera to get some tissue. When he comes back he acts like it never happened. 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 possesses Jack and jumpscares the viewers. The words on the whiteboard are now scribbled out. Anti jeers the viewers, blaming them for Jack's death. He says the viewers could've stopped him from doing it, but they just watched. Finally, the video cuts to black and ends.
In January 2017, the all too familiar static and sounds can be heard in Jack's videos.
On 28th July 2017, Markiplier made a video on his channel titled "DARKIPLIER vs ANTISEPTICEYE". During the video, the two were arguing about who should be "king" of their "realm" (dubbed "YouTube Hell" in the comments). The two were about to fight, however they were constantly disrupted by other YouTubers dark sides (ABlazingPhil (AmazingPhil), DannyDarko (DanTDM), Sharkyoho (Schmoyoho), etc). Then Chica, Dark's dog, appears and sucks the other dark sides into a void. She becomes angered, saying that Dark didn't feed her. As Dark panics, Anti stares at the screen (actually staring at Chica), laughing. Anti played a more insane role than a serious one.
On 3rd August 2017, Anti appears in Bio Inc. Redemption. At the start of the video, Jack explains that the developers made an Easter egg of him in the game. Then he starts feeling 'sick', so rushes off camera. Doctor Schneeplestein replaces him and vows to save Jack in game. Halfway through, Dr Schneeplestein himself complains of discomfort and makes references about death and Anti (such as 'antidepressants'). Anti glitches into the facecam and game more frequently, taking over Dr Schneeplestein. When in-game Jack finally dies, Anti appears. He berates the viewers by saying he's tired of repeating the same cycle (to quote: "How many times must I do this? Again and Again! OVER and OVER! FUCKING CIRCLES!") meaning he is tired of killing Jack just so Anti can appear to please the audience. He also mimics the viewers when they nickname him "glitch bitch" (a name fans gave him online). He poses a few questions, such as "who do you think you've been watching all this time?" responding with "my puppets." He states that this is his world and this isn't the end of him. The video cuts to black as he giggles and says "see you soon."
-DARKIPLIER vs ANTISEPTICEYE (crossover)
It's time to DIE!
You wanted me, well here I am.
You could've stopped me, but you just watched, as this happened!
You found someone to replace me, threw me aside.
Always there, always watching
You're weak, just like HIM!
Why don't you put on more makeup? I've already won!
This world is mine! These people are mine!
Why didn't you feed your dog?!
I am in control!
That "doctor" thought he could save him, but he was mine! He was WEAK!
Mocking me with your "glitch bitch"
I am eternal!
I'M in control!
Who do you think you've been watching all this time?
Just my puppets
If you want him back so badly, then why don't YOU save him?
This is my world!
Well there are no strings on me
I wonder what will happen to your favourite BOY next time
This isn't over
See you soon
Ỉ̌͌ͬ̚͟ ̘ͣ̂̃ͥ͌̿ͬs̸̹̗̖͇̣̞e̥̻͓̭͕͛̾̚ê̼͖̹̌̌ͥ̕ ̗͙̹̦ͬ̔́y̝͕͗̏̒ͮ͢ͅo̖̤͉̼̘͖͎ǘ͓̭͔̀.̪̐ͦ̊.͉̙̞̺̪̪̽̓ͨ̑.͍̰̺͖͓̤̘͌̇̓̽̓͞
n̯̻̦ͮ̄͋ǒ̯̯̱͗̚ ͙̳̰ͦͦ̒ṃ̟̘ͯ̉͛ọ͕̣̐ͪͤŕ̘͓̈̑ͅê͇̘̙ͬ̌ ̙͍̬͌̅ͤg̜͉̤͌ͪ̓a̜͕̹̐͋ͨm̲͈̯̉ͦ̚e̤̝̤̒̂̈́s̪͚͈̄ͦ̎
I͔̮̘͙ͮͮͅt̮̻̯̱̻̠̲̉ͣ͐͜ ͓̱̟̤͚̭̱ͬ͗ͫ̎̐̒̀i̖̝̥̮̗̱̹͊͊ͮ̌̐s̷͉̠̥͔͛͛ͬ͒ͣ̚͞͡ ̡͖̮̆̓ͦ͝d̰͔͈̰̣̃͌ͫ̂̊͊̉́͟o͚̜̩̯̺͍͗ͮ̑̉̃̕n͖͔ͥ́͝ẽ̴̳͕̹͙͇̝͓̘̕
a̲͇̹̟̫͕ͫͣͦ͑r̷̛̤̞̻̒̇̃͑̀ͫ̌̔͢ͅé̷̯̩͈̹͉̮͔̪̇ͨͨ͑ͧͨ̌̄ ͥ̈́̒̒̾̒͟҉͓ẙ̷̡͈̱̠̫̗̉͐̊͌ͩ́ͅo̝̬̞͈͓͔͙̪͉ͬ̊ͪͬ͒ͫ̿̿̉u̴̠̫̺ͪͬ̐̋͐ͧ̈ͣ͢ ̟͓̟͉̞̙̐ͮ͠ŗ̶̟̟̮̩͓̎͋͝e͚̰͆̂ͣ̏ͩắ̉ͭ҉̞̝̥͉̰͎d̷͙͇ͬͬ͆̇̍ỷ̺̻̟ͫ́ͤ̓̚̕?̪́̎ͥ̕
I miss the piercings
Trying to grow the beard out!
Ze good doct͏͠à̷h
A̧̡͜nd Ǹ̡ow T̸̀̀͏empting Í͟nside