Minecraft wiki entry for List_of_broken_features, associated text: When a snow golem was built, along with the snow golem, a cloak of snowflake particles would also be generated around it. Similarly, when building an iron golem, a burst of snowball-textured particles would also be created at the instant of its spawning. In 12w18a, these particles would no longer appear at all, and the mobs would just phase into existence with no further effects.