I realize that Falling Star is banned in all sanctioned formats, but suppose in a casual game, I cast it and then choose to copy it using Fork. When the copy of Falling Star resolves, does anything actually happen?

With no card to represent the copy on the stack, my best guess is that you can't actually perform the action of flipping it, and the remainder of its effect doesn't apply. (or I guess, since you can't satisfy the condition of turning it completely over, the no effect clause takes place.)

As Callum said in this post and this one, too: we don't entertain questions from the deepest, darkest corners. This forum is designed to help judges learn about the rules and card interactions that they'll need to judge tournaments.

I suppose that, in a casual game, the answer is whatever your casual group agrees to.

d:^D