onEvent('worldgen.add', event => {
  event.addLake(lake => { // Create new lake feature
    lake.block = 'minecraft:diamond_block' // Block ID (Use [] syntax for properties)
    lake.chance = 3 // Spawns every ~3 chunks
  })

  event.addOre(ore => {
    ore.block = 'minecraft:glowstone' // Block ID (Use [] syntax for properties)
    ore.spawnsIn.blacklist = false // Inverts spawn whitelist
    ore.spawnsIn.values = [ // List of valid block IDs or tags that the ore can spawn in
      '#minecraft:base_stone_overworld' // Default behavior - ores spawn in all stone types
    ]
    
    ore.biomes.blacklist = true // Inverts biome whitelist
    ore.biomes.values = [ // Biomes this ore can spawn in
      'minecraft:plains', // Biome ID
      '#nether' // OR #category, see list of categories below
    ]
    
    ore.clusterMinSize = 5 // Min blocks per cluster (currently ignored, will be implemented later, it's always 1)
    ore.clusterMaxSize = 9 // Max blocks per cluster
    ore.clusterCount = 30 // Clusters per chunk
    ore.minHeight = 0 // Min Y ore spawns in
    ore.maxHeight = 64 // Max Y ore spawns in
    ore.squared = true // Adds random value to X and Z between 0 and 16. Recommended to be true
    // ore.chance = 4 // Spawns the ore every ~4 chunks. You usually combine this with clusterCount = 1 for rare ores
  })
  
  event.addSpawn(spawn => { // Create new entity spawn
    spawn.category = 'creature' // Category, can be one of 'creature', 'monster', 'ambient', 'water_creature' or 'water_ambient'
    spawn.entity = 'minecraft:pig' // Entity ID
    spawn.weight = 10 // Weight
    spawn.minCount = 4 // Min entities per group
    spawn.maxCount = 4 // Max entities per group
  })
})



Valid biome categories (#category):

taiga
extreme_hills
jungle
mesa
plains
savanna
icy
the_end
beach
forest
ocean
desert
river
swamp
mushroom
nether
This is the order vanilla worldgen happens:

https://mods.latvian.dev/link/28#bkmrk-raw_generation-lakes
 
raw_generation
lakes
local_modifications
underground_structures
surface_structures
strongholds
underground_ores
underground_decoration
vegetal_decoration
top_layer_modification