Nazo

Nazo is an overarching antagonist in the SMK series. He is a entity made of pure negative energy and the former 8th Chaos Emerald. His main motive is to have more energy so he destroy the Master Emerald by destroying Earth. He is also one of Sonic's greatest enemy.
== History ==
Nazo is made up of pure negative energy, whereas his brother is a Wave Demon. Negagen, his younger sibling, constantly strives to outdo him, but no matter what he does, Nazo always manages to come out on top. Surprisingly, Negagen managed to escape the war, while his brother ended up being imprisoned.
== Personality ==
As a being born from negative energy and pure chaos, Nazo is not only naturally evil but also highly destructive and chaotic. He seeks to absorb as much energy as possible and make sure he's the most powerful entity in existence, and he will kill all who stand in his way or serve no purpose in his mission.
He erased Metropolis off the face of the Earth purely to test his new level of power after taking a silver emerald and was going to destroy the Earth via destroying the Master Emerald (which holds infinite power and thus would remain superior to Nazo no matter how much energy he absorbed, something he couldn't tolerate since he, in his own words, will not be damned to eternal subordination towards that rock), then presumably go on a rampage across the Universe. In spite of this, according to Chakra-X, he holds some slight respect towards Knuckles for being the guardian of the Master Emerald, hence why he didn't kill him (though it's also possible he may not have been strong enough at the time).
His motives are more unclear in the original The Power of Nazo animation, but he's more respectful, saying he's honored to meet Shadow, and less murderous and violent.