How do I

Based on the image below, how do I create a indicator to show where the enemy is going to fall before you see enemy on screen? (for example arrow in red)

https://www.dropbox.com/s/2k3pzjny81qsp ... 2.png?dl=0

You could actually do this in a lot of ways depending how your game is set up.

You could have a 'detector' sprite just above the window which, when an enemy enters it, spawns the arrow directly below on the screen before the enemy enters the screen.

Alternatively if you are spawning those enemies right above the window, you could simply spawn the arrow at the same time with the same X but a greater Y.

So... When enemy collides with another object ... spawn arrow at Player.X -, Player.Y - 100. Something like that...

Could I see the example so I can have a better a idea.