So, as you may or may not know, the way Minecraft generates worlds is through a density function which uses noise to assign every coordinate a specific value. If the value is positive, then there will be a block there. If the value is 0 or negative, there will be air there. This pack multiplies that density function by -1 right at the end, for all three vanilla dimensions, so that everywhere with air is instead a block, and everywhere you would expect a block is air.
I'm sure that you can imagine the consequences of this.
