minecraft-assets/data/minecraft/worldgen/configured_feature/crimson_fungus_planted.json

{
  "type": "minecraft:huge_fungus",
  "config": {
    "decor_state": {
      "Name": "minecraft:shroomlight"
    },
    "hat_state": {
      "Name": "minecraft:nether_wart_block"
    },
    "planted": true,
    "stem_state": {
      "Name": "minecraft:crimson_stem",
      "Properties": {
        "axis": "y"
      }
    },
    "valid_base_block": {
      "Name": "minecraft:crimson_nylium"
    }
  }
}