Solaris

Solaris is by far the most powerful being to appear in the (canon) series so far as it took three Super Hedgehogs to defeat him and even then they couldn't actually destory Solaris (as Solaris by this point is effectively omnipotent and immortal) so ultimately they did the next best thing; they destroyed his core which leaves him alive but powerless (as he can't control his body). Solaris was a god of time and the super-dimensional sun god of Soleanna seen in Sonic the Hedgehog, who also looks similar to Perfect Chaos. Solaris initially existed as a flame which was worshiped by the citizens of Soleanna. The Duke of Soleanna led experiments into Solaris, in the hopes of using its time control powers to allow humanity to correct its past sins (and also to allow himself and his young daughter, Princess Elise, to see Elise's deceased mother once again). However, during one such experiment Solaris became unstable and split into two forms - Iblis, the raw power, and Mephiles, the conscious mind. Mephiles was sealed into an artifact known as the "Scepter of Darkness" whilst the Duke was forced to seal Iblis inside of Elise's soul. Before dying from wounds caused by the accident, he told his daughter to grow up to be a strong queen who would never cry as doing so would destroy the seal on Iblis.

After killing Sonic, Mephiles was quick to rejoin with his counterpart, once again forming their complete form of Solaris. Plunging the world into darkness he prepared to devour time itself. Before he could achieve this, he was defeated by a combined assault from Super Sonic, Super Shadow and Super Silver. His defeat spirited Elise and Sonic back to before the fateful experiment. After some contemplation, Elise chose to blow out the tiny flame that was Solaris and thus change history by erasing him from existence.

During the battle with the three super form hedgehogs, Solaris attacked shooting out meteors and firing a large laser that can hit it's enemies from any distance. He increases the number of meteors and laser he fires in his second form (he can fire out 6-14 lasers). Solaris is one of the few bosses in the series whose attacks take rings away from Super Form characters, and the only boss that doesn't use different attacks when it changes to a different form. Another power Solaris has is during the "End of the World" level (where the characters are trying to revive Sonic), is to create massive orb-like "eyes" that suck in anything around them, including enemies the characters encounter. Touching the eye results in instant death, regardless of rings or even an invincibility power-up. He also has red eyes that he uses to hurl objects at his enemies.

Trivia

 * Solaris is the second boss who can do any actual damage to a super form. Each of his attacks costed Sonic, Shadow and Silver 10 rings.