Super custom worlds

a more simple version of the old custom world type feature but now in game and not importing a file. Allowing you to edit the frequency of mobs and structures, and the split chances for all the biomes (yes i know biome chances would mean that now the 18 quintillion seeds would such skyrocket). Would be cool for challenges like a no structure challenge, too many outpost challenge, creeper spam challenge. Understandably the one mob unremovable is the ender dragon.