Minecraft wiki entry for Before_1.18, associated text: The mushroom field shore was a technical biome that represented both the shores and the rivers of the mushroom fields. It generated when a river cus through it as well as when it bordered an ocean, unless the ocean was a deep variant, in which case a steep cliff generated instead. The terrain of this biome was much flatter and shallower in elevation, similar to beaches, though it was equal to the mushroom fields in every other way. Buried treasure and shipwrecks generated here.