Hi eolelake,
I'm not sure I understand your question. I'm assuming that by "randomly dropping" you are suggesting, that a sprite will start at a different location each time it moves from the top of the Scratch stage to the bottom.
You could start out by coding something like this for your 'dropping' sprite:
[blocks]
<when green flag clicked>
<forever>
<go to x <pick random( -240 )to( 240 )y 200
<repeat until><( <y position> <<> -180 )>
<change y by( -5
<wait( 0.1 )secs>
<end>
<end>
[/blocks]
(okay, I've had it, these forum blocks are horribly buggy and frustrating!)
This should make your sprite move in a straight line from the stage's top to the bottom at a fixed speed.
Then you could experiment with the numbers to make the sprite go faster or slower, and add some other movements to - maybe - increase the sprite's speed as it keeps falling ('gravity') or to also make it go sideways.
Did that help?
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