Nazo the hedgehog

Nazo is a very rare type of character... a non-character! Nazo is a light blue glowing character that showed up in a Japanese trailer for the Sonic X series. This mystery character never actually ended up in the series, and the producers never explained who this was supposed to be. Since the character doesn't exist, he also doesn't have a name. The name "Nazo" was given to him by fans, and simply means "mystery" in Japanese.
Fan Creation
Since Nazo was never officially used, fans used this opportunity to make up their own stories involving this unknown hedgehog. Most well known of the Fan creations, was the popular Nazo Unleashed flash series created by Chakra-X.
Nazo's Forms
Normal Nazo - The base form of nazo, also the first form we see. Though, This is the weakest of his forms, he is still able to over power Sonic, Knuckles, Tails, and Shadow in their normal,base forms. But it is shown that he is soon outclassed by sonic and shadow when they power up to their super forms and team up together.
Perfect Nazo - After being beaten by Shadow and sonic, Nazo takes the Chaos Emeralds, and goes back to Angel Island. With the Master Emerald back in place, the island begins to float once more. Using Chaos Control, Shadow takes the gang to the island. Knowing that he can't beat them with his current power, Nazo absorbs the power from the Chaos Emeralds, transforming himself into what he calls "Perfect nazo". With this transformation, Nazo's fur is red, he has more spike protrusions, his shoes are black and yellow, his eyes are red, he has yellow cuffs, and the outside lining of his eyes are red. He has the ability to use "Super Chaos Control" with over-rides normal Chaos Control. While in this form he easily defeats Super Sonic, and Super Shadow. He even survives a full power chaos blast by an enraged Dark Super Shadow, without even a scratch.
Hyper Perfect Nazo - After taking a beating from hyper shadic, Nazo informs Shadic that he has only helped him get stronger by changing the Chaos Emeralds into Super Emeralds. Nazo then preceeds to absorbs the new reservoir of negative chaos energy eminating from the Super Emeralds. His general apperance doesn't change much. Instead of red eyes, he now has blue, his shoes are black with a triangular yellow mark on the front of them, his cuffs are now black, and the outside lining of his eyes are now black. With this new power, he is nearly right on par with hyper shadic, even almost winning the power beam struggle. Thanks to knuckles and tails, Nazo gets distracted for a moment, and shadic shoots all of his energy at once, over-whelming nazo. Nazo survives, only to be killed by Shadic, after Shadic reverts Nazo back to his normal form and blasts him with one last powerful energy attack.