Old Customized

Old Customized (known as Customized prior to 20w21a) was a world type that allowed players to thoroughly customize the terrain generation of the Overworld. The ability to create Old Customized worlds was removed in 18w06a with the rewrite of world generation. A new world type known as Buffet was added to replace it in 18w16a, though the only configurable options were biome and terrain shaping type. A new format for Custom worlds was added in 20w21a.

There were 18 customization options that affected whether structures generate, among other environmental factors.

The decrease in the frequency is not linear: the difference between 1% and 25% is huge, the other differences up to 100% are minor.