The problem: Apparently some extremely knowledgeable technical Minecraft coders were digging into the code and found that the random number generation routine that is called when certain structures are loaded has a major flaw - the random number seed is based on world seed and is the same every time the structure loads. What this means: All events based on this random number generation will happen the same exact way each time the chunk loads - including how many pieces of ore will drop from a specific block using a Fortune 3 pickaxe, how fast a specific wheat plant will grow and where a specific mob will spawn. How the exploit works: When certain large structures are generated, the world random number seed is re-set to a value based on the world seed. This causes a "Groundhog Day" effect starting at that moment and until the user's actions re-scramble the random number seed. For example: You are elytraing through the sky and suddenly everything stops for a second or two. A Woodland Mansion has just been loaded and all the surrounding chunks get reloaded and the random number seed is reset back to this specific value I've been talking about. You look on top of the hill and see a creeper. That creeper will appear in that spot every single time the woodland mansion is unloaded and reloaded into memory. So you decide to build a tiny little 1-block farm right at that spot. Just 3 blocks of cobble, 1 sticky piston to squash it and a hopper beneath it feeding a chest. Okay - but it's too much work to keep loading and unloading a woodland mansion: The evil beauty of this exploit is that there is a redstone circuit that will automate the loading/unloading of those chunks in such a way that on every game tick the chunks reload and a new creeper is spawned at that exact same spot. Why you bringing this up?: I would hope that this exploit will be looked for and eradicated should anyone try to use it. Not only is it a terrible cheat, it is extremely taxing on server resources.