Skull Skull Fall
Stack the skulls in groups of 3 or more to make them disappear. Careful, don't let them rise above the safe area. Have fun. Position the skulls of the same color so that they form a group of 3 or more elements that are connected horizontally or vertically.
Such a group will free up the space it's taking up and earn you points.
If even a single skull stops in the red region it's game over.