I transfered my single player Minecraft world to my home server so that I could play survival multiplayer with my roommate. One major issue that I encountered was that hostile mobs started spawning on the top of trees. Normally this would not have been an issue except I happen to have a massive artificial forest in my main home, let’s call it a wildlife preserve. I happen to like my wildlife preserve but abhor the idea of creepers falling from trees killing me and damaging my precious forest. Luckily I found a Bukkit plug-in that stops mobs from spwaning on trees. Disaster averted.