The golden blob continuously reappearing within the core that was being rebuilt to perfection countless times was the essence of Ken's soul. The process itself was cultivation and every time he had a breakthrough, he reached heights he hadn't ever before.
The black mucus oozing out of his body were the impurities that had been gradually accumulated within, from breathing, drinking, eating, accumulating mana, every intake had certain amount of impurities within them and were stored when accumulated or consumed, such impurities accumulated over the years were now being gradually pushed out of his body.
Every breakthrough was an extremely difficult process that would take a lifetime for a few without talent, but with his [Abyssal] trait and experiences, breakthroughs weren't that difficult.
The strands of mana concentrating at the sides of his forehead were his now-growing horns, which currently were merely bumps.