Animation with image_index

if vspeed_ < 0 sprite_index = sprSquidSwim else sprite_index = sprSquidFall
image_speed = 0
image_index = 0

if round(image_index + image_speed * sprite_get_speed(sprite_index)) < image_number {
    image_index += [ANIMATION SPEED; just mess with this a bit until it looks right; should be <= 1]
} else {
    image_index = image_number
}

draw_self()