minecraft-assets/data/minecraft/worldgen/placed_feature/twisted_potato.json

{
  "feature": "minecraft:twisted_potato",
  "placement": [
    {
      "type": "minecraft:count_on_every_layer",
      "count": 1,
      "start_offset": 0
    },
    {
      "type": "minecraft:rarity_filter",
      "chance": 13
    },
    {
      "type": "minecraft:biome"
    }
  ]
}