The ink

The Ink is an infection-like phenomenon that was first spotted attached to Fluffy's face. In one of Billy's recent lore streams, the stream ended with Billy being trapped by the Vanguard Clan in the room where The Ink was being contained. It is presumed that Billy will be The Ink's next victim, since at the very end of the stream, Billy's voice could be heard saying "Goodbye good Billy." Billy, in a 3rd person description, describes it as 'very toxic' and 'burns when you touch it.'

Basic Information
The Ink was first seen on Fluffy's face after Fluffy was absent for one of Billy's streams. The Ink acts as a parasite—attaching itself to a host which it then seems to take control of over a period of time. The Ink was initially found by Fluffy while they were trying to expand the mountain area rooms. It seems that when someone comes in contact with it, The Ink will stick to the victim's skin, and then start to harden, making it nearly impossible to remove. The Ink also seems capable of corrupting it's victim, assumed by the phrase "Goodbye good Billy," which was heard at the end of one of Billy's lore streams. The Ink has many unique and potentially destructive qualities. The Ink seems prone to catching fire, and has even been witnessed to start fires if it becomes too dry.

The Ink seems to consist of dark shades of wool and coal blocks, both of which have been seen on-fire. The effects of The Ink 's possible corruption is still unknown. Some have speculated that influence from The Ink could've been what led Tusco to betray Billy, but this hasn't been proven correct or incorrect just yet.

Scrapped Lore
(Thank you to Fluffy for providing this information) Fluffy was originally going to run away from Billy's house, due to fear of what the ink on their face was going to do.

Fluffy had prepared a skin where their character was shown wearing a purple cape. This skin would've been used to watch over Billy from a distance, since Fluffy still cared for Billy and wanted to make sure he was okay.

Fluffy also planned to have a scene where Billy would notice Fluffy, and attempt to confront them.