Mobs (short for mobiles) are moving entities that can be killed. There are four types in Pocket Edition: Passive, Hostile, Neutral and Utility.
Update 0.12.1, most Mobs drop Experience, with the exception of baby animals, Villagers, Squids, and Bats.
Passive Mobs ignore the Player and run away if attacked.
Hostile Mobs pursue the Player if they are close enough (however, in Creative Mode, they behave like Passive Mobs).
Neutral Mobs attack the Player only if aggravated.
Utility Mobs can be created by the Player and attack Hostile Mobs.
Mobs tend to drop
Items that can be used for Crafting, Eating, or Smelting.
List of Mobs
Creepers drop 0-2 Gunpowder, 1 Creeper Head (if killed by a Charged Creeper).
Silverfish drop nothing.
Skeletons drop 0-2 Arrows, 0-2 Bones, 1 Skeleton Skull (if killed by a Charged Creeper).
Slimes drop 0-2 Slimeballs.
Zombies drop 0-1 Iron Ingots, 0-1 Potatoes/ Carrots and 0-2 Rotten Flesh, 1 Zombie Head (if killed by a Charged Creeper).
Blazes drop 0-1 Blaze Rods.
Magma Cubes drop 0-1 Magma Cream.
Ghasts drop 0-1 Ghast Tears and 0-2 Gunpowder.
Stray drop 0-2 Arrows, 0-2 Bones.
Husk drop 0-1 Iron Ingots, 0-1 Potatoes/Carrots and 0-2 Rotten Flesh.
Wither Skeletons drop 0-1 Coal, 0-2 bones, and 1 Wither Skeleton Skull (if killed by a Charged Creeper).
Witches drop 0-1 Stick, 0-1 Glowstone, 0-2 Sugar 0-1 Redstone, 0-1 Nether Wart and 0-1 Spider Eye, and drops the Potion it was using as an equipment drop.
The Wither drops 1 Nether Star when killed.
Elder Guardians drop 0-1 Wet Sponge, 0-1 Prismarine Crystals, 0-1 Raw Fish, 0-2 Prismarine Shards.
Guardians drop 0-1 Prismarine Crystals, 0-1 Raw Fish, and 0-2 Prismarine Shards.
Endermites drop nothing. (Upcoming in Update 1.0)
Shulkers drop nothing. (Upcoming in Update 1.0)
The Ender Dragon drops a Dragon Egg. (Upcoming in Update 1.0)
Skeletons, Zombies, and their Nether variants can spawn with equipment, Armor (usually leather, chain, or gold) and have an 8.5 percent chance to drop each piece. They are more likely to spawn with items in Hard mode, or a full Moon.
Iron Golems drop 3-5 Iron Ingots and 0-2 Poppies. Its drops aren't affected by Looting enchantment. Naturally spawned Iron Golems can become hostile, if the Player irritates the Villagers.
Snow Golems drop 0-15 Snowballs.