Don't forget the most important mob...
The Steve is the most dangerous creature in Minecraft. Nothing you can do will permanently prevent a Steve from entering your house and taking your items: the Steve is capable of opening any door, knocking down any wall, and harvesting any block. Steves can open your chests and rifle through your sock drawer. Steves have been known to set traps, using explosives or dispenser blocks. (Let me tell you... fire arrows shot from a dispenser block HURT!) Steves carry a variety of weapons: swords, picaxes, bows and arrows, sometimes even just a sharp stick. Some Steves, of the "griefer" subspecies, carry buckets of lava and are capable of setting objects on fire.
It's not all bad, however. The Steve may often be a very helpful creature: other Steves have been known to help mine, fight off skeletons and creepers, and even donate materials to your Giant Fortress of Fun.
The Steve is also the only creature in Minecraft that you can talk to. Pressing the T key on your keyboard allows you to engage a plain-text chat system. Your words are parsed through a Turing algorithm and passed to the Steve's natural language processor. If the other Steve chooses to respond, you may get a helpful response like "wan 2 teem up?" or a hurtful one like "die noob."
Danger Factor: High
Helpfulness Factor: High
Armor: bare flesh, leather, metal, diamond
Weapons: fists, sword, bow, magic potions, pointy stick, fire
Drops: random loot; possibly any kind of item in the game
Special abilities: mines any kind of block, has the power of speech
Vulnerabilities: lag, harsh language, /kick
Recommendation: talk first, be prepared to run away