It's a sketch of a new fusion I've made up. I haven't drew the wings yet.

"The true fusion form of the three hedgehogs of the past, present and the future. It was prophesied that when these three combined, a forbidden being would be born, causing devastation when untamed. A seraph in one part, a demon lord on the other and a cosmic body at the last, Neutron is known as 'The True Ultimatum'."

However, he is not entirely immortal... He can still be injured and heal fast but only be killed by another half-angel, half-demon

This can only be achieved if the three are in the most devastated state of emotion, obtaining the previous memories of the first Neutron (He was called 'Nebula'), and by collecting not only the Chaos Emeralds, but also the seven deadly sins and seven significant virtues. Soon, it's easier if they can obtain Mephiles' permission to unlock the gate of the forbidden (In which, Mephiles doesn't appear physically, but mentally.)