After many conversations with Clockwork, Danny decided to be his apprentice, partly because Clocky was the closest thing he had to a grandfather, and partly because he really wanted to travel back to the time of the dinosaurs.
Clockwork was well aware of that fact, which is the reason he made his lessons as difficult and cryptic as possible. And although it frustrated him, in the end Danny succeeded. Due to his core, at the end of the lessons he ended up becoming the "Master of Space", which was not the same as Clockwork but quite similar.
He didn't realize that being a "master" of literally anything was lonely. They also didn't inform him that being a halfa would give him immortality, Danny sighed sadly, at least Clocky kept him company.
Perhaps the reason for his future actions was due to that feeling of loneliness; After watching a new dimension being created, both Clockwork and Danny witnessed a baby wizard being born in Egypt on that dimension, he had immense potential (Danny found it curious that many events tended to repeat themselves as a constant in the progress of different dimensions, like the egypt creation for example)
Since he had never witnessed anything like this before and it reminded him a bit of Tucker, the Master of Space went to congratulate the little wizard. But when he said goodbye, he followed him! Like a duckling. Danny saw this and plead his mentor for help, Clockwork just shook his head, Nabu would be a future lord of order, but right now he was just a curious and lonely kid (and Danny got a headache thinking about the intricacies of the dimension).
Resigned, Danny stayed in Egypt for a couple of hundred years, he began to teach Nabu space magic and other arts he had learned over the years; Clockwork seeing that his apprentice had taken his own ward, decided to taught Nabu a bit about future vision, a useful gift for the boy. When Nabu eventually disappeared, they both decided to leave without leaving a trace behind, it was like they never existed, even if the people remembered them.
Danny just didn't expect his little Nabu to have turned into a ¿spirit? trapped in a helmet and other artifacts thousands of years later, of course he'd made some dubious decisions but thats was a little cruel for a punishment, even if he was not sure if Nabu did that to himself; The halfa felt lost, there was no manual of "I met my pupil after a long time and he is trapping people with his helmet and other objects to possess them"!? He swears, he checked on Ghostwriter library!
For their part, the Justice League was confused when the respectable and usually unflappable Dr. Fate began to jump on his heels impatiently as he looked out of the Watchtower, waiting for something, or rather someone.