Since the Past Mistakes AU shows Red and Solomon's early lives, I imagined there being a part of it showing Zachary's early life, such as his love for the Godzilla series, the NES Game, etc.
Plus I also included him wearing that striped shirt from the Entropy TV screen (shown below) since he said that he had a shirt that looked just like that when he was a kid. Another reference to the Creepypasta is where he said that he'd doodle in his notepad whenever he was bored.
So, yeah. That's pretty much it.