Insane Refinement
"Hammer!" Krune shouted as he picked up all the 700+ Nightmare Cores using Mental Energy before making a cluster with them. His Star Hammer then unleashed a powerful gravitational force, siphoning it from the three rings of his Star Ring enveloping the room.
The gravity was then used to compress the Nightmare Cores as lightning flickered through them, beginning to melt them. A day later, all the Nightmare Cores had been melted and reshaped into a massive core.
Through Mental Energy, Krune extracted all the negative emotions contained in them, sending them towards the center, where they were condensed to the extent they turned ethereal.