Begin any Day Stage. A split-second after Sonic says "Go", press Circle. This will give you an extra Dash and an extra Boost to your meter. If you press Circle when he says go, you will get a Dash start, but no boost, so watch the timing. If you dash too many times before Sonic says "Go", then you could trip and lose seconds.
Sonic UnleashedMore guides, cheats and FAQS