here is a screen fader demonstration. feel feel to use it in your projects. switch backgrounds with the space bar. so this project basically follow this concept to fader backgrounds: you have one sprite and the stage with the same costumes in the same order, then when you want it to fade, the sprite sets itself to the next costume with the ghost effect at 100 (hidden) then slowly decreases the effect until it is visible, this creates the effect of fading. once its dont fading it tells the stage to switch to the backgorund the sprite is on and then the process repeats agian.