I finally stumbled across a zombie spawner in a Minecraft world, so I was excited to try constructing a trap to run them all to their deaths and get some of that sweet loot. I did a lot of research online, and found that a lot of the water traps shown in videos etc were for such old versions of the game that a lot of them simply didn't work anymore. For some reason, it seems that it just isn't possible to drown mobs. I also learned that it simply wasn't possible to make a zombie trap that produced loot! In the case of zombies, they don't drop loot unless killed by a player. So the key is to use water to push zombies down a drop that causes them to lose most of their health so that they can be slain with single blows. Looking into this led me to a super fun solution, which is to use water to raise the zombies up to the height of the desired drop, then push them over to the drop. This is called a 'Mob Elevator' and it magically uses a feature that mobs have that if they are in water, they jump up. You then use another practically insane feature of Minecraft that a sign will prevent water from flowing past it to create a tube with alternating blocks of water and air. The mob enters a suspended block of water, jumps up until they rise out of the next block of air into the next block of water, and then the cycle continues. The resultant motion beautifully looks like they are simply levitating! Then you put a horizontal channel at the top with water that pushes the mobs to the drop. At the bottom of the drop, which needs to be slightly less than 22 blocks, there needs to be something to block the mobs from escaping, with an opening for poking them with a sword. Here are some links that show the design:
The best design I found. Some designs had wide riser tubes with alternating water blocks, but I found that the tube only had to be one block wide:
http://www.planetminecraft.com/project/survival-mob-grinderxp-farm/
The link that showed alternating water blocks unnecisarily, but still shows a good outlibe of the shape of the elevator connected to the drop:
http://minecraft.wonderhowto.com/how-to/exhaustive-guide-building-mob-traps-minecraft-0131112/
Ideas that didn't pan out for me:
Cactus traps. Pushing mobs into cactii kills them, but apparently they don't drop their loot when they die:
http://www.minecraftforum.net/forums/minecraft-discussion/suggestions/13719-cacti-shouldent-destroy-items-on-contact
Lava Blade: Again does a good job of obliterating mobs but then I don't get the loot or XP:
http://minecraft.gamepedia.com/Tutorials/Mob_grinder
http://minecraft.wonderhowto.com/how-to/minecraft-monster-slaying-slice-your-enemies-with-deadly-lava-blades-0135146/
Drowning traps that didn't work for me. I couln't get them to drown, but more importantly the zombies didn't drop anything except rotton meat:
https://m.youtube.com/watch?v=c6Fz7u7hTIw
