Every decision has an alternate ending—every alternate ending includes its own timeline. Thus is the Strings Theory in it's simplest terms—or, at least, the way I learned it.

CLOCKWORK'S DOMAIN—GHOST ZONE—AFTERNOON

"Danny!"

Clockwork watched expressionlessly as the majority of Daniel Fenton's enemies zapped him simultaneously with ectoplasm. When the boy began to glow with the power, Clockwork froze time.

He determined that the little ghost energy left within that stripe of seemingly harmless white hair had reacted—it would either spread its power to the rest of the boy's system and return humanoid, or it would start the process and, using the surplus energy around them, combine into the boy's former Halfa appearance.

Clockwork examined the two alternate timelines carefully—the latter seemed to have virtually no harm to it whatsoever. Powers regained, the boy would rally the ghosts and save earth—and, by extension, the Ghost Zone—from the Ectoranium asteroid.

The former, however…It seemed dangerous—Clockwork would need to keep a wary eye on it. Perhaps even as wary an eye as the timeline with Dark Dan. If one of the frequent visitors of Amity Park were to truly find a way to obtain a Host…

That decided, Clockwork gave the Halfa an extra boost towards the latter timeline and returned to his domain to watch the other timeline.

The two were identical at first—but where Samantha Manson and Daniel Fenton got together in the chosen timeline, they didn't in the alternate. Where Daniel Fenton and Danny Phantom were exposed as the same being in one timeline, the world remained oblivious to this fact in the other. Where Vladmir Plasmius was banished in one timeline, he returned to the ghost zone in the alternate. Where Daniel seemed unchanged in the chosen, he became almost unbalanced in the alternate—for that simple stripe of different colored hair seemed to be more important than first examinations.

It seemed that through that stripe of purest white, the Human side of Daniel became stronger—and through the stripe of darkest ebony, the Ghost side of Daniel became weaker. By the time Daniel Fenton was twenty years old, he would no longer require a transformation to access his Ghostly Half—the two would have merged into one entity.