Scratch

So you can change the speed also, make a variable, (speed). Using the equation, speed = distance / time (where distance is 480 pixels [the width of the stage]), we can change the speed of the sprite.

forever
set x to (-240)
set y to (pick random (-180) to (180))
glide ((480) / (speed)) secs to x: (240) y: (y position)

Try changing the speed variable and see what effect it has and adjust it how you want. Setting x to (-240) will reset the sprite to the far left of the screen every time it reaches the right side. Picking a random Y value will mean that it appears at a different location on the same side of the screen every time as required.

If you have any related questions, ask away on this thread!

-Prestige 

show

This will show a sprite on the stage.

hide

This will hide a sprite on the stage.

You can use the 'glide' block as seen in my earlier reply so the sprite will glide across the screen. Just remember that the stage is 480x360 pixels wide, so if you want a sprite to move from left to right they'll go from x=-240 to x=+240:

set x to [-240]
glide (2) secs to x: (240) y: (any value)

Hope this helps you