Son of Nightmare was born from one of the tears Nightmare shed upon his destruction mixing with one of the power stars shot from the Star Rod. This is a fact that Son of Nightmare is embarrassed by, as no self respecting Nightmare should ever cry. Least of all in the face of someone like this. Overall, SoN doesn't think too highly of his now deceased father (who can now materialize in a spectral form, but has no power and can't interact with anything).
If the real Blade Knight inc user name was used as a troll account, Son of Nightmare was used a the "totally random" account, and because of this, Son of Nightmare can be quite chaotic in series, especially given the combined powers of a Nightmare and the Star Rod. However, he seems to be more self obsessed with proving himself to other people, and belittling others. Son of Nightmare in the series is far more snooty and uppity than weird and random.
In fights against common Dream Land adversaries, he tends not to get involved, as he just doesn't care what happens. After all, he's much too important. Cosmic forces that threaten the planet are another matter entirely, as they are a threat to his livelihood or continued existence. He will side with good during these battles. And while he doesn't exactly commit evil deeds, he's not above putting one over on someone else just so he can get ahead. That's just the game of life, man.
Son of Nightmare is absolutely obsessed with Pokemon battles. It is currently unknown why this is... but if a certain currently running comic's story would be continued on, I could fill out the rest of this paragraph with the reasons.