Agor.io
From Screamer Wiki
When you open this, a picture of Jeff The Killer Pops up with a ear-piercing scream that inverts negativity at a seizure inducing rate, and when you try to close the website, a pop up happens and says 'U SCARED BRO LOL'. Obviously, whoever made this is some troll.
Media
There are multiple social media posts such as this one on Reddit about the site. This one in particular was supposedly written by a parent whose nine-year-old son had an epileptic seizure when trying to play agar.io because they misspelled it as agor. The mother states she is talking to a lawyer and is attempting to track down and prosecute the creator of the Agor.io website.
