So Jack kinda died from Billy, re-lived a day in his life (judging by what happened it was before he found the secret entrance).

Then he kinda realized that he was hallucinating (around the part he got out of the car).

He woke back up, the illusion faded and both Mark and Jack were "super saiyan" and its awesome. Jack, in this new level of power (which is green, not blue) can now control characters powers too. AWESOME YOU GO BOI.

That's it I think.