Minecraft wiki entry for Building_a_metropolis, associated text: Block Limitations: To force more creative use of specific blocks (especially important since using fewer blocks improves the quality appearance of a build), the player could force themselves to only use specific blocks or to not use blocks that usually show up in their builds. Sometimes, using specific blocks could act as a way of theming or adding a story to the city. Possible limitations might limit the material, color, or rarities of blocks used. Another variant is to only use blocks available in a certain version, for example only building with blocks available in Classic.