Act 1 is a tutorial-like stage. Focus on getting used to Sonic's speed and the Homing Attack. You'll encounter your first White Wisps to fill your Boost Gauge. The main path is linear, but keep an eye out for springboards leading to higher routes. There are 5 Red Star Rings to collect. The first is usually on a higher path after a series of springs. The second requires a well-timed Homing Attack chain. The third is often hidden behind a destructible wall (use Boost). The fourth might be on a lower, less obvious path, and the fifth usually requires a precise jump or a quick step. Practice your quick steps to avoid obstacles and maintain momentum.
