(See the best response by Kaiochao.)
Hi guys, i'm currently working on a soccer game, so to break the monotomy of the ball always moving straight on the ground, i'm implementing an "elevation effect" to the ball.

The problem is, i'm using the shadow as an underlay, so each time that i increase the pixel_y value the shadow comes with the ball. My english is not the best, so to illustrate what i want to do i will leave an image here :

How can i do this ? Maybe an object that moves together with the ball ?
Best response
Either apply the opposite pixel_y to the shadow, or yeah, make it a separate object that moves right after the ball moves.
In order to apply the opposite pixel_y i will need to remove the current shadow underlay, create another shadow image decrement or increment the y value and add to the underlays again, right ?

In your opinion what is the best way ?
Instead of using an underlay, use a separate /obj instance and have it follow the ball around (What Kaiochao said).
Ok, i will try !
Problem solved, thanks guys !