Bubbles

Bubbles is the unofficial name given to a character briefly spotted a couple times in the 18th video in the series; Run in Circles. The name holds no relation to any official information released about this potential character as nothing is definitively known about them outside of one background appearance. The name was decided by members of the Hiding in my Home Discord server as a placeholder name until any official identity is revealed.

Information
Little if anything is known about this character. Bubbles is seen for less than a second in the background of Run in Circles (18), and the image has to be brightened for details to become fully visible.

Bubbles's existence was acknowledged by Anthony in video 21 (Strategizing), confirming Bubbles to be a character in the series. Anthony suspects Bubbles to be the owner of the residence Hollis is currently staying in. Anthony is unsure if Bubbles is intentionally helping Hollis or if Bubbles is unaware of his presence. (As Anthony previously claimed to be.)

Of course, with nothing but one short and obscured appearance lacking in detail so far, there is no way to discern any definitive information about Bubbles as a character. Nevertheless, there has been no shortage of theories.

Speculation
Many theories revolve around the idea that Anthony and Hollis are not the only two relevant individuals influencing events within the story. It is suspected that there may be some 'third party' who is either aiding one of the two individuals, working against one of the two individuals or manipulating them both for their own ends. If this theory is correct, Bubbles would make a prime suspect.

While the screenshot is obscured, this must be put into perspective - most other minor characters in the series such as the neighbours get nowhere near as clear an appearance, thus suggesting that Bubbles may indeed be a relevant character. This is further supported by Anthony dedicating a significant portion of video 21 to speaking about him, something he has not done for any other background characters thus far. If Bubbles is indeed an important character, he would fit the position of this 'third party'.

If Anthony's claims that Hollis murdered Jordan are to be believed, then Bubbles' role would likely be of a co-conspirator aiding Hollis in his crimes. Whether their relationship is of two willing criminals or one murderer and one reluctant lackey is unknown. It is equally possible that Bubbles is completely unaware that any of this is happening and does not know Hollis is currently residing in his home. It mustn't be forgot that Anthony claims Hollis was living on his property for over a month without anyone realizing. In either case, their inclusion in video 18 would've likely been an intentional effort on Hollis's part to further taunt Anthony.

If Anthony is assumed to be lying and the real villain of the story as some theories speculate based on his suspicious actions in videos 14 and 19, then it is possible Bubbles is a friend of Hollis helping him escape Anthony, either merely for Hollis's safety or in an attempt to expose Anthony's wrongdoings. In this case, their inclusion in video 18 would've likely been a mistake by Hollis, not realizing an image he included revealed his friend/accomplice when brightened.

If both Anthony and Hollis are assumed to be at least partially innocent, then it could be theorized that Bubbles is the true villain of the story, manipulating the two for their own ends. In this case, it is possible that video 18 is either Hollis attacking Anthony for crimes he believes Anthony committed but in truth were the work of Bubbles, or might be a direct attack on Bubbles which Anthony misconstrued as an attack towards him. If the latter is true, it is questionable why Hollis would not have explained this in video 20, but perhaps he is unable to speak openly about Bubbles. He had mentioned many times in video 6 and others of his inability to fully explain the situation at hand.

A less popular theory suggests Hollis may not have uploaded videos 15 and 18 at all, and that they were instead uploaded by Bubbles either as attacks on Hollis or to frame Hollis for attacks on Anthony. In either case, their inclusion in video 18 would've likely been as a form of taunting either Anthony, Hollis or both.

It is likely that as the story progresses, it will become more clear whether Bubbles is a relevant character or merely an innocent bystander. If the former is true, many more theories about his identity and role in the story are likely to emerge as more information is revealed and disproven theories are likely to be rejected with time accordingly. For now, we can only run in circles.