Minecraft wiki entry for Beating_a_challenge_map, associated text: These include soul sand, ice, and vines. Soul sand makes you walk slower through an area, ice makes the ground slippery, and vines can be distracting when fighting against walls. Although these will not directly kill you, they can be a pain if you're trying to do something risky, such as fighting mobs. Therefore, try to stay away from soul sand or ice, and avoid being cornered by mobs in a vine-filled area.