There are lots of how-to-make-scrollers tutorial projects out there! Just search for "scroller tutorial" on the Scratch search, and you'll find one!
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Well, i don't think this belongs here. It should belong under all about scratch, i'll just tell a mod.
so, as guinea_pig_girl said, there are tutorials on this topic. the main thing is that the character doesn't move; the background does. make the background move when you press the button, so then you get a scroller! add jump features and other stuff, and you have a game! of course, the "other stuff" is the hard part...
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There are plenty of tutorial.
Basically you have everything in the character the same as a normal platformer, except where it changes the X, make it change a variable called scrollX or something.
The background sprites then go to that variable, plus or minus a certain amount depending on where they are.
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http://scratch.mit.edu/projects/platform710/1242224 this is a base I made, it might help
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Everybody above covered it.
-12three-
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