Minecraft wiki entry for Gathering_resources_on_peaceful_difficulty, associated text: Wither skeletons, when killed, rarely drop a wither skeleton skull, which can be used to make the wither boss. Unfortunately, wither skeletons don't spawn on Peaceful, and they are the only way to obtain wither skeleton skulls. The only use of wither skeleton skulls is to create the wither(the Wither cannot spawn in peaceful anyway so there would be no point), or as a helmet. The wither drops a nether star, which can be crafted into a beacon. This means that beacons are one of the items that cannot be obtained on Peaceful difficulty. However, conduits, a similar block, are obtainable and constructive on Peaceful. A conduit requires a heart of the sea from buried treasure and 8 nautilus shells from fishing or bought from wandering traders, as well as prismarine block variants or sea lanterns to active it.