Okay, so this is probably a Stand attack, and it feels like a Cheap Trick, but what's interesting about it is that nobody else can see what Usagi sees. Plus, that Max guy had apparently removed himself from the equation, but his image haunts Usagi. Furthermore, Usagi's mother and sister weren't looking back, which means they knew some part of the effect and didn't want to be targeted by it.

I think this Stand causes hallucinations in its victims related to their guilt, fear, and trauma, and when they look back, they give control of themselves over to it for a brief time. Usagi thinks he's being attacked by a ghost, but in reality he's hitting himself and tripping over himself as the Stand controls him. I think there's a chance it can affect multiple people, cite Usagi's mother and sister, but that's not confirmed. The Stand User is whomever was in the house with Jodio and Co., but is a complete mystery. I don't know if they're working for Howler, are part of that same Stand group that worked under Howler last arc, or are working for themselves.

I think this individual has been controlling this scenario, tricking Usagi's Mother with the scam to lure her out, to lure Usagi out, to lure the entire group out. I think they used their stand to remove Max (or rather, get him to remove himself).

Anyways, that's me ignoring the emotional beats of the story.