shadow, having decimated the Black Arms forces in Westopolis, destroying a fleeing tank of theirs and A Black Bull, proceeds on to Circus Park, where He's searching for that "Damn Fourth Chaos Emerald". Upon arriving he sees Tails crash the Tornado, and heads after him. Tails, once shadow finds him reveals that he came here to retrieve all the rings that Eggman stole, since they are being used to power this version of Eggmanland. Eggman, however shows up on one of his floating tv's and asks shadow for his help in defeating the invading GUN geeks, who are ruining his park and destroying his precious robots.

Tip: There's an extra shooting gallery behind the key door if you need it, but the hero mission really isn't hard enough to warrant needing it. 

Circus Park is really Circus. Even the music Hammers that in. The Rings mission seems to generally be hated because of how it is plot and gameplay. And I get gameplay, but they're called Power Rings for a reason, they are what give enough energy to keep super forms going after transforming, they are extremely powerful.