Creeper are the HB-men of Minecraft. They literally blow up at every little thing. Creepers seem to suffer from sociophobia and fear of humans, because their detonation is caused by human presence and is announced by a hissing sound, which is caused by the frying fat inside the creeper. They always walk in the green tobacco leaf cloak (again, a reference) through the world. Somewhere it was said that the appearance of the Creeper came from a failed attempt to model a pig. There's not much of a resemblance there. The original purpose of the Creeper was to sneak up behind the player and detonate before the player is out of range. The probability to do this is higher the closer you are to a lava pit and the more diamonds you carry.
Zombies are actually humans who have been infected by a strange disease. This causes them to stink of old swamp, make strange bubbling noises and have the urge to infect other people with the disease. Other people with the disease. However, they only manage to do this to NPCs who are far too stupid to run away from the zombies quickly enough anyway. If a zombie cannot infect its victim, it simply kills him. The tool used to spread the disease and kill is the zombie's spasmodically forward-pointing arms, which also serve to mate the zombies. Zombies, in fact, have an abnormally high sex drive, which is probably related to the zombie's disease.
Skeletons are deceased chemistry teachers who return to the world of the living to throw pixelated sticks at the player to make him die. Often, however, they didn't hit the player because, as you know, skeletons don't have eyes. When the game developers noticed this, the skeletons were reworked and now it is practically impossible to dodge the arrows.
Spiders are strange black 2x2 block sized boxes that move at high speeds because they burn inside their pixelated shell, which can be seen through their eyes. The oxygen needed for this blackening procedure is supplied by the open eyes, which are also used to release steam if it accidentally gets too hot. This phenomenon produces the often audible hissing.
Slimes are the bouncing sadomaso popel Minecrafts. They spread like guinea pigs when hit and prefer to die in lava.
Giants are basically giant effigies of zombies. They are totally tramp-like, which many a addict has witnessed. Giants like to live as individuals and always have huge precincts, which explains why you never come across them.
Endermen are 3-block high creatures that teleport so they can attack you from behind (if you are lucky and have 50 diamonds, you will always be pushed into lava by them), which is why some call them "campers of Minecraft". They have extremely long arms and always look stupid, and they also destroy your house by stealing your blocks, because they can't build one themselves, especially if you're still a Minecraft noob and build your house out of earth, because Endermen stopped stealing stone or wood some time ago. Endermen have their own dimension, the End."
Ender dragons are the relatives of the Endermen. If you let them loose on the normal world, they destroy everything in sight, only their world is spared (that was obvious). If you defeat the end dragon, it explodes and you can return to the normal world, but you have to wait for decades because the story of Minecraft, the credits and some stupid saying at the end of the credit flood come first (unless you press the ESC key, which almost nobody does).
Lava slimes are slimes that burn in hell. They consist of several layers like a cake. If you defeat them, they quadruple and the game starts all over again. At some point there are so many that you get crushed.
Also from hell are these cuddly blocks, which are a cross between commercial zombies and pigs. They are created by the increased sex drive of zombies mentioned in the "Zombie" section, which have the dominant role in mating. Upset Catholics claim this is also the reason for staying in hell (Also called Nether or support group against weird grunting and hypersexuality). Sodomy simply does not befit religious circles. The behaviour of the zombie pigmen towards the player is rather neutral. They only attack when provoked or when the player is not at the computer. This then results in the loss of all items, which all burn in the lava or are sold by the zombie pigman on Ebay. When they attack then preferably in groups, they simply feel stronger that way. Therefore, we have reason to believe that Pigmen are aliens.
Ghasts, a emos favourite mobs, are square giant lumps who probably used to work in the car press, hence their shape. With a few mangled tentacles, this monster can fly from right angles for some unknown reason. No matter what you do or where you are, you can expect to be stalked by at least 10 ghast, who are about as intrusive as insurance salesmen after lunch. You don't know much about the Ghast other than their name, family, friends, career, whereabouts, mobile and landline numbers, and favourite foods and habits. What all Ghasts have in common is the validity of the motto: "After three days, Ghäste and fish stink".
The Wither is practically Fluffy. The only differences to the likeable little dog from Harry Potter are that he flies, is black, has a completely different shape and can fling his three heads around. Afterwards, of course, they grow back again. The player can build it, as it's the only way to get a Nether Star to put in the unnecessary Beacon block. (I'm still sure Jeb meant to write "Bacon Block".) The Wither is also a way to fat grieve.
Herobrine is, according to legend, Notch's dead brother, whom many sources say he incorporated into his game. He (Herobrine) actually looks quite normal, but you can recognise him by his white glowing eyes - So you can be Herobrine yourself, if you have only looked at yourself from behind so far. Herobrine's behaviour is more reminiscent of that of a small child, as he kills everyone (for no reason) by digging them into the ground one by one and using only redstone torches, although these are known not to be a good source of light. However, Notch has programmed Herobrine in such a way that he himself cannot remove him from the game, which can be seen from the fact that Herobrine is removed (again) in every update. Maybe this is the reason why most people have never seen Herobrine themselves - but maybe not.
Chickens are definitely the most horrible monsters in Minecraft. They don't attack you, but they spread like only chickens in Minecraft because they lay eggs that you throw and chickens come out of again. Also, they can be semen pairs, of which you have far too many anyway. Because of this creepy reproduction method, they are definitely monsters. They often appear in caves (also called Evil Chicken). And that's that.