bedrock_roof_position: The distance from the world height for the top coordinate of the bedrock roof, if out of world bounds (0-255) the roof does not appear, example: "-1". e.g. setting this to 32 puts the top of the roof at y=224. If the bedrock roof is low enough, natural terrain still generates above it. [needs testing]
bedrock_floor_position: The y coordinate of the bedrock floor, similar to bedrock_roof_position – setting both floor and roof to 255 generates a single layer of flat bedrock for each of them. [needs testing]
sea_level: The sea level in this dimension between 0 and 255
disable_mob_generation: Can be true or false. [needs testing]
structures: Structure settings
stronghold: Settings for how strongholds should be spawned. The stronghold values under the structures tag appear to be placeholders so that every namespaced structure has a value; these values are the ones that actually control stronghold spawning.
distance: Controls how far apart the strongholds are. [needs testing]
count: How many strongholds to generate. [needs testing]
top_slide: Settings for the curve at the top of the world.
target (integer): The value of the curve. Negative values round off the top of the hills in the affected area, positive values create a roof. Higher values produce larger effects.
size (integer): Defines the size of the affected area from the top of the world. size is calculated using the formula size = <height in blocks> * 0.25 / size_vertical.
offset (integer): Moves the affected area from the top of the world. offset uses the same formula as size so offset = <height in blocks> * 0.25 / size_vertical. For top_slide, positive values move the area down and negative values bring it up.
bottom_slide: Settings for the curve at the bottom of the world.
target (integer): The value of the curve. Negative values remove the floor and round off the bottom of the islands, positive values make a floor. Higher values produce larger effects.
size (integer): Defines the size of the affected area from the bottom of the world. Uses the same formula as in top_slide.
offset (integer): Moves the affected area from the bottom of the world. Uses the same formula as in top_slide. For bottom_slide, positive values move the area up and negative values bring it down.
xz_scale (double): Scales the X and Z axis of the noise. Higher values results in more intricate horizontal shapes. Works similarly to coordinate scale from old customised worlds.
xz_factor (double): Smoothes the noise on the horizontal axis. Works similarly to main noise scale X/Z from old customised worlds.
y_scale (double): Scales the Y axis of the noise. Higher values result in more intricate vertical shapes. Works similarly to height scale from old customised worlds.
y_factor (double): Smoothes the noise on the vertical axis. Works similarly to main noise scale Y from old customised worlds.
size_vertical (integer): Changes the Y scale of the landmass. Values between 1 and 15 gradually increase the hill height, above 20 are all above the normal sea level of 63, and higher than 32 give normal land levels of 100+.[needs testing]
size_horizontal (integer): Changes the X/Z scale of the landmass, but not the biomes.[needs testing]
height (integer): Changes the max height of generated terrain by squashing the world. For example, with height=128, the ground is set to Y=32. this does not affect sea level.[needs testing]
density_factor (double): Changes the gradient of terrain density from the bottom to the top of the world. Positive values result in a world that is solid underneath with terrain shapes that shrink at higher altitudes, negative values result in a world that is solid on top with empty space underneath. Greater positive or negative values result in a sharper transition.
density_offset (double; values between -1 and 1): Moves the center height for terrain density, by an amount inversely proportional to density_factor.
island_noise_override (boolean; optional): Causes the world to generate like The End with a big island in the center and smaller ones around.
amplified (boolean; optional): Toggles between amplified and normal terrain generation. Can be used alongside large biomes in `vanilla_layered` types, and in any dimension (Nether, End, and custom).
↑Setting this to a number does not mean one structure is generated this often, only that the game attempts to generate one; biomes or terrain could lead to the structure not being generated. The maximum distance of structure placement attempts is 2*spacing - separation.