Perhaps have a "wall" effect like Super Mario Bros - so you can't travel off the screen back where you were?

If character going rigth to left moves backwards it may give player impression that he is rewinding the story. If you make all the game assets on the right to left moving player act like that i might give a good traveling to past impression.

I don't know what kind of story are you trying to tell so i cannot give an input on that aspect ( If that is what you want )

1. Make the left/right characters visually distinct.

2. On the introduction of the left character, give the player a REASON to move left.

3. On the introduction of the right character, give the player a REASON to move right.

For example, in the earlier games without tutorials such as MMX, there's a wall to the left and an open highway to the right. Why would you move left? The only viable path is to the right. It's open and it looks safe.

Im making a simple enough platformer but I have written a good enough story I think. Its split between two characters. One you play standard left to right but the other I plan to have right to left. The significance is you are going back through that characters story. I was wondering do you think this is clear or would I need to make it clear to the player how the story was being told.

Just to clarify for my own confusion. When you refer to the second character moving back through the first character's story. Are you referring to the idea - that the results from the first character's travelling is what the second character will encounter. Or, alternatively, are you referring to a situation such as reversing time as you travel back through the first character's story.

I find the idea of a 2 direction game interesting if only for ideas such as: in investigating a series of crimes (committed by the first character), a detective (second character) might retrace the path of what has happened trying to unravel the why what etc of the results and in essence recreate the knowledge of a specific timeline and the events there in.

Perhaps have a "wall" effect like Super Mario Bros - so you can't travel off the screen back where you were?

Speaking of Mario, I read something interesting a while back (I don't recall the exact source, sorry): If memory serves, the game was not originally conceptualized to scroll only to the right. This was actually implemented as a trick or shortcut to minimize system resource usage (once an area of the game is loaded and passed, it can be disposed of and never read again).

Sorry ya I should have stated that the player will be forced to move right to left. Theyll be started on the right and blocked off from going right. I meant more in terms of a player understanding how the story is told or would they get a bit lost.

Why not just make the players play through the levels in opposite directions of each other? Player A begins a level at the "entrance" and finishes at the "exit". Player B begins a level at the "exit" and finishes at the "entrance". Then you don't have to limit scrolling direction, which would give much more freedom of movement to your characters. If there are puzzles or other obstacles, it may be necessary for the player to run around, back and forth, until they figure it out.

That's my $0.02.

Most people just naturally go right

You can look at maps of six flags and you'll find that the path on the left is almost always larger while the path to the right is almost always smaller. They do this to avoid large groups of people going in one direction and forcing longer lines. http://mappery.com/S...-Theme-Park-Map It's incrediably obvious in this map, on the path to the right from the entrance they block it a bit with shrubbery, AND they hide the open expanse after the right path with rides. While the path on the left opens up to multiable paths and is an open-ish expanse with multiable paths.

Also from a level design perspective if you want a level to be easy to navigate you're going to add more Right hand turns with the left hand turns being dead ends. If you want a level to be harder to navigate you're going to add more "proper path" left turns than right turns. You're welcome to go into games and count the number of right/left turns, it's also especially noticable on Halo levels.

To be honest If a character only has Right to Left platforming that character won't be nearly as liked as the Left to Right character.
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To sum it up Left and Right is a pretty big deal. Edit: I recomend having a major story element tied to it just to make your game memorable, something absurd/mind blowing/whatever.