Sonic Axiom

Sonic Axiom is a Sonic the Hedgehog fangame assembled by Me
and released in its latest form in 2011. Its game engine is based on the fan-made Sonic Worlds engine.

Inspired by the design of the classic Sonic platformers, Sonic Axiom distinguishes itself with fantastic visual aesthetics (albeit many of those modified from pre-existing resources), impressive and diverse level design, and a huge amount of content for a fangame: Three playable characters (Sonic the Hedgehog, Miles "Tails" Prower, and Knuckles the Echidna), eighteen full-fledged levels, nine bosses, and seven original special stages, each with a Chaos Emerald you can collect or ignore.

Dr. Robotnik is back to his old tricks, turning animals into robots, industrializing pristine environments, and generally making a mess of things. Are you a bad enough 'hog to teach him a lesson?