How do you beat Solaris in Sonic the Hedgehog 2006?

In phase 1, you start with sonic as you know, switch to Silver immediately and keep deflecting the asteroids thrown at you by solaris and firing them back at his arm, one that breaks, switch to Shadow and keep using Charged Chaos Spears until his other arm is broken. You are now left with Sonic to attack the core, I recommend charging before dashing toward Solaris so you have less chance of getting struck by the lazers. Once you take all his health down, a cutscene will occur.

After this cutscene you will be in Phase 2, in this phase you need to use all 3 heroes, in whichever sequence you like, be mindful of rings and in time you will beat Solaris.

I Hope this helps :]