Passage of time ingame , fades in and out at certain trigger volumes.
Credit to Sega and Sonic Team for the Sonic Model and level textures
Credit to Ghost , the1 , SonicXtreme and Calico , SonicTag, Dazman , TheDragon , Kirby_422 , HDoan , M4573R51337 , Dominator , SSDC , RandomHaloGuy , Killa.
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