Minecraft wiki entry for Creating_behavior_packs, associated text: Events can use a randomize function to pick between different results (see "minecraft:entity_spawned" in pig.json). Note that the weights for randomize can add to over 100. This is because they are not percentages! If you set the weight for making an adult pig to 23 and then the weight for making a pig baby to 100 then you will have a 23/123 chance of getting an adult pig and a 100/123 chance to get a baby pig when a pig is spawned.