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I think you did a great job with this tutorial, although I would have a slightly different approach.
Instead of cycling through every object that draws a shadow behind and initializing it's shadow script, I would instead make a parent object for all the objects that you can place in-game and in the parent's draw event, draw the shadow (don't forget to draw the object's sprite first!).
So now all objects that is a child of the item's parent object will automatically draw it's shadow without the need of tediously cycling through what could be 50+ items.