Someone made a Sonic romhack called Hellfire Saga and the FM synth work goes absolutely feral. Built on Genesis sound hardware, this soundtrack pushes the YM2612 into territory that feels genuinely threatening, which is wild for a Sonic game.
Read more
"Forest of Decay" escalates across its acts, each version adding layers of urgency. "Sin City Act 1" has this gritty bassline that sounds like Mega Drive metal. The final boss theme takes the title track and cranks everything, two phases of pure intensity.
"Spirit World" breaks the tension with something eerie and floating. Even the microboss and miniboss themes have distinct personality. If you think Sonic fan projects can't surprise you anymore, this soundtrack is your wake-up call.