I'd like to cover a topic: Mob farms. Mob farms are obviously used to get XP fast, and many players use them. Some spawners are easier to make into a grinder than others. For example, a zombie and skeleton grinder are pretty much the same, but a spider spawner and blaze spawner are both completely different. Zombie/Skeleton Spawners: Spider Spawners: Blaze Spawners: Ender Man Farm: Zombie Pigman Farm: (Note: this person made a pretty big farm, which most people would like, but it requires a lot of obsidian, and a smaller version could be made by halving the dimensions.) Info on Mobs: Zombie, skeleton, and spider kills all give you 5 XP each mob killed. Blaze kills give you 10 XP, plus, the blaze rods they drop can be used for furnace fuel, and they are more efficient than coal. All mobs are killed if dropped by 22 blocks, meaning if you were to make a grinder where the mob dropped, they would have to drop 21 blocks, so they would be killed. A half-slab counts as a full block in this situation, so using one would not change the fact that the mob would still die. If you wanted an automatic XP farm, your taking the "XP" out of XP farm. Automatically killing mobs with blocks, pistons etc doesn't allow you to collect XP. Meaning that by dropping a mob (i.e, zombie) 21 blocks would leave it at around 1 heart. Which means you can kill the zombie or skeleton with one punch, instead of a few sword hits, saving your resources. Ender men farms are pretty difficult to make, considering they will attack you unless you wear a pumpkin on your head. An efficient way to make an Ender man farm is to make them drop, and many farms have piston activated blocks so they could farm ender eyes and XP, or just ender eyes. Pigmen farms can be made in the Nether or Over world, whereas the nether is more dangerous, considering you have ghasts. TIP: Only people with the 'Silk Spawners' ability that is purchasable from the store can break or place spawners. Hope this helps if your trying to make a mob farm!