Ever played a game called Worms? You know how when you hit the ground, it darkened those pixels and made then un fit with collision? So like, if you walk into a part thats been shot(It looks like a hole but it's actually the pixels that got darker), you wont collide with the pixels that are darker.
I'd love for this feature to be in GE, allowing you to make a digging game or a game where you have to blow up stuff.