How do you complete all the levels in Shadow the Hedgehog for the PS2?

Answer 1

To unlock the stages play through a different story each time you play, as for walkthroughs of every stage, look up the stage your stuck in on YouTube or try a site like IGN for written guides by fellow players.

Answer 2

when you go to different missions like good or bad you get to new levels if you press start and hit Y on the game cube game it will show u the route on which mission go to.For example: when your on the first level you will have a chose whether to kill the gun soldiers or the black monster or get the chaos emerald if you successful complete on mission in the story mode it will take u somewhere new. hope this helps :D