Guest 666

Guest 666 is an old Roblox myth and creepypasta who was rumored to have admin commands in any games they joined (even ones without admin built in), and whenever a player hovered the mouse over a guest image when viewing game servers, their name used would appear as "An Evil Guest" instead of "A Friendly Guest" like it normally does.

Overview
It is assumed that Guest 666 looked the way any normal guest would (which changed multiple times with various Roblox updates), but some people portray them as having black skin and blood red eyes.

History
Unlike other myths, there isn't an exact date available that could tell when the myth came into existence. It's possible that the legend was going around ever since guests were created in 2008, making it one of the oldest myths to date.

Many alleged Guest 666 sightings exist on YouTube.

Soon after its inception, the myth was proven to be false as it turned out that you could use browser extensions such as Edit This Cookie, which allowed you to change your guest ID, and doing, one could become Guest 666. This did not grant the legendary Admin abilities that Guest 666 supposedly had.

After Roblox announced the removal of Guests in October of 2017, the myth itself largely ceased to exist as it was impossible to see or play as Guest 666 following the update.

Behavior
It was said that Guest 666 would use admin commands and chat when in-game, which was something normal guests couldn't do. However do to the myth being fake it is very likely these are all just speculations and rumors.

Unlike the other guests, Guest 666 was supposedly capable of using chat to view messages and talk themselves.

Trivia

 * Guest 666 was popularized by big Youtubers such as ObliviousHD, who made a series of videos about him in 2017, amassing over 25 million views in total. His game "ObliviousHD Roleplay World" also allows you to summon Guest 666, who can kill you if he catches you. Both surviving and being killed, as well as summoning him, give you badges.
 * There are also two other games centered around the identity of Guest 666, amassing over 4,5 million visits in total.
 * There is a badge dedicated to Guest 666 in the game "The Myth Hunt" developed by Enszo.
 * Interestingly, both registered users by the names of Guest_666 and Guest666 are banned. It's possible that those users might've been exploiters who tricked people into thinking that they were actual guests, which caused their termination.