Mobs
"You don't know what mobs are? It's that thing behind you about to eat your brain." - 
Acsidol
Mobs or monsters are an integral part of the survival aspect of Minecraft. They come in different flavours, some aimless and passive, and some united in a single cause come nightfall: to bring about your swift demise, amongst a chorus of ill-choreographed hisses, growls and clanks, accompanied by the occasional bang.
Note that server-exclusive features not available in vanilla are included. Those looking for server-exclusive mobs should check the Dungeons page instead.
Nocturnal Mobs
"I really hate cleaning all the rotten meat off my roof in the morning." -
M_Fujiwara
Most nocturnal monsters spawn at night or in darkness.
Zombies
Zombies shamble around, make unnaturally loud growling noises, and are either undead Steves or villagers. They attack by attempting to give you zombie hugs, and will also attempt to break wooden doors. However, because the difficulty is "normal" in the overworld, they can't succeed. On death, they drop worthless rotten flesh, which will end up clogging your chests if you have a grinder. They also have a chance to drop iron ingots, the armour they're wearing, carrots, and potatoes. Sunlight causes them to burst into flames and eventually die, though being attacked by them while on fire will set you ablaze as well. Zombies will attack villagers as well, and can zombify them instead of killing them. These zombie villagers, which sometimes spawn naturally, can be cured with a golden apple and splash potion of weakness.
Zombies are generally a low-level threat unless you are cornered by them, and more of a nuisance on MCO. The greater threat they pose is the lag their path-finding AI can cause in large groups, and thus large grinders of them are not recommended.
Zombies also come in some variants. Baby Zombies are a threatening existence and extremely annoying due to their fast movement and high intelligence. A desert variant of zombies are called husks.
Skeletons
<RepulsiveCurve> i got hurt and no sekeltons <Rayzion> what are sekeltons >? <RepulsiveCurve> a monster .... <Madjock999> a 5 year olds spelling of skeleton? <RepulsiveCurve> with bows <Rayzion> dude your an idiot <RepulsiveCurve> hmm <RepulsiveCurve> sek? <RepulsiveCurve> for short?
Skeletons are armed with a bow and an unlimited supply of arrows, and their presence is signalled by bony clunks. They tend to keep a range from the player, firing incessantly, making them harder to use close-range attacks on. Skeletons drop bones, which can be used to make bonemeal, which is a white dye and miracle grow for your garden. They also drop some of their arrows, so you're armed for the next time the blighters come back. Occasionally, they will also drop their bows and their armour. Skeletons, like zombies, burn when in sunlight. The ice variant of this - stray - will also burn by sunlight.
Skeletons are an annoying pest on MCO, but the lag often cripples them and makes them easy to defeat without taking damage. Skeleton grinders are commonplace, and thus ammunition and bones are as well.
In 1.12.2 Freedonia, thunderstorm rain caused skeleton horses to spawn and when struck with lightning, spawned armed skeletons riding on undead skeleton horses. This was a very annoying situation which occurred during mid-2021, causing uncountable numbers of death.
Spiders
Spiders are horrifically enlarged arachnids that make hissing noises, and attack by leaping and biting. They can climb walls and fit in one-block-tall areas, so remember to block windows to avoid unwanted night visitors. Spiders are hostile when found in darkness, such as at night or in caves. However, in the light, they become neutral and will only attack if hit first or if they were already attacking you. Once killed, spiders drop string and/or a spider eye. Spider eyes are useful in brewing, while a string can be used to craft wool, fishing rods and other items.
Spiders are just as crippled by the lag as any melee mob. They can be killed by a single critical Sharp V diamond sword swing, or a fully charged Power V bow shot, making them less of a pain for experienced players to remove.
Cave Spiders
Cave Spiders are the small spiders found in mine shafts that poison you on contact. Much more dangerous than regular spiders, but if you've found them you've found a free spawner.
Creepers
"That'sssss a very niceeeeee everything you have there, it'd be a ssssssshame if sssomething were to happen to it..."- Anonymous creeper
Creepers are phallic green suicide bombers, and will silently walk up to you before hissing and exploding. For most of Freedonia's history, creepers were nerfed - they would approach you for a hug, but disappear harmlessly, failing to do any damage with their explosions. This was necessary to avoid people abusing them to grief structures. With the option present to remove any mob's ability to damage blocks, creepers can now explode and harm players but not structures. As a result, creepers are once again scary.
If killed without exploding, creepers can drop gunpowder, which can be used for TNT. Given that TNT cannot break blocks in Freedonia, gunpowder harvesting is nearly pointless, except for crafting fireworks in preparation for events or elytra flights.
If a creeper is hit by lightning it will become charged, vastly increasing its damage potential at the cost of some of its HP.
Endermen
Endermen are tall black men added to Minecraft in the beta 1.8 update. They will scream and attack players who look at them, dealing a fearsome amount of damage and frequently teleporting behind the player. Their block-carrying ability has been disabled in Freedonia to prevent them from griefing player structures. Endermen will randomly teleport short distances and will do so instantly when hit with projectiles, making them susceptible only to melee attacks. Endermen will also take damage from water. When killed, they may drop ender pearls, which can be used by the player to teleport themselves to the location it lands when thrown, and also to craft Eyes of Ender, which are used to craft ender chests. Endermen spawn in large amounts in the End dimension.
Ender pearls are very valuable and frequently used, so endermen should always be slain on sight when possible.
Witches
Witches are the evil version of villagers, and use potions to buff themselves and attack players. They are very dangerous and a pain to fight, as they will heal themselves constantly, slow/poison/damage you, and make themselves speedy and immune to fire. Upon death, they drop sticks, various brewing ingredients, bottles and/or the potion they were drinking when slain.
Witches are a good source of various mid-level resources, but annoying to fight and quite rare. The best approach is to attack them at a distance outside their aggro range, or try and kill them as they're healing for a free healing potion.
Slimes
Slimes spawn in caves at any light level, or in swamp biomes at night, where their spawn rates are affected by the phases of the moon. When you kill a giant Slime, it will split into smaller parts of itself, which upon death can split again. However, tiny slimes don't split when killed and instead drop slime balls upon death. Slime balls are used to craft sticky pistons, leads, and slime blocks.
Large slimes can be a good source of XP, as each death will yield more orbs. Their high damage might make using a bow a smarter choice for this. Recent slimes can swim in the water, so a slime farm in Freedonia usually comes with magma blocks and Craftbook's Chest Collector IC.
Silverfish
Silverfish are tiny grey bugs that hide inside stone blocks in extreme hill biomes and strongholds. When you hurt a silverfish, but don't kill it in one hit, other nearby silverfish will break the block they are hiding in and attack you. This process can even destroy normal stone blocks nearby to summon more silverfish. They can also hide in any stone, stone brick or cobble blocks they find. Silverfish do not drop anything when killed. This mob is extremely rare in Freedonia due to the low amount of strongholds, and most people using mob spawners for other mobs.
Bats
Bats spawn in dark caves. They will sleep upside down on the bottom of blocks, but fly away when a player comes near them. They do not drop anything upon death.
Bats are known to inadvertently make their way over to players, and annoy them by blocking block placement or taking hits from tools meant to be mining blocks.
Husks
Zombies in the desert biome are different from those in other regions. They have sun-protecting clothes to prevent burning under the sunlight, and the rest is the same as regular zombies. When killed they drop rot flesh, sand and other rare materials. They are very useful for sand farms, as zombie spawners in desert biomes spawn husks. It cannot spawn elsewhere.
Strays
Strays are ice cold-hearted (if they even have hearts anyways) skeletons living within ice biomes. They can burn under sunlight, but the difference from regular skeletons is that they wear clothes to survive freezing environments and slowness arrows, making arrow-to-arrow combat better for killing strays. They drop bones, normal and slowness arrows and gravel when killed, which makes players create gravel farms with its spawners.
Polar Bears
Ice-type bears may spawn in Ice Plains biomes, though they are scarcely ever found in Freedonia due to the low amount of habitat snow locations. They attack players if angered in some ways but otherwise roam around, sometimes in a pair or with their child.
Nether Mobs
"I hate Ghasts! " - 
Zen_Fighter
In the realm of the Nether, there are five powerful mobs that you will likely encounter. Many have died because of them.
Ghasts
Ghasts are giant, floating, tentacled ghosts that moan and shoot fireballs at the player. They are the most dangerous mob in the Nether. As well as their high mobility and range, they can see you from one hundred blocks away and deal enough damage to two-shot a player in full Prot. IV diamond armour. Luckily, their Fireball can be deflected by hitting or shooting it, and they can be killed by a single charged bow shot. The block-destroying fireball they shoot has been edited to not destroy blocks or start fires, though it will still break paintings and item frames. When killed, they may drop gunpowder and ghast tears.
Due to their incredible damage, caused by a mod which spawns an exploding TNT minecart where their fireball impacts, you must avoid getting hit at all costs. During the rare moments when the ghasts aren't slowed by lag, they are killing machines.
Zombie Pigmen
Zombie pigmen are a combination of a zombie and a humanoid pig, carrying gold swords and making snorting sounds. Pigmen will spawn in small 'tribes', so there are usually a couple around the same place. They can run quickly, and deal significant damage. They are neutral mobs, only being angered by hitting them. But be careful when killing them, as all other zombie pigmen in a large radius area will aggro as well and come to help their brethren. This usually results in you being violently assaulted by ten angry zombie pigmen. They drop gold nuggets, rotten flesh, and very rarely golden swords and armour, and ingots upon death.
In previous versions of MCO, when a player is killed by another in PVP, a group of Pigmen Police in blue uniforms with wooden swords would spawn and investigate the player's death. If you attack one of the officers they will group together and fight you. These officers do not drop anything upon death. This was replaced with Steve Police on 1.12.
Magma Cubes
Magma Cubes are like slimes except more damaging - even the tiny ones will deal damage - and capable of jumping higher. When you kill a giant magma cube, it will split into smaller parts of itself, which upon death can split again. Like slimes, tiny magma cubes don't split upon death and instead drop magma cream.
Blazes
Blazes are the rarest mobs in The Nether. They will only spawn from spawners inside nether fortresses or rarely, on their own inside the fortress. When they see you, blazes will start floating upwards and will throw three fast, undeflectable fireballs at you in rapid succession. Once thrown, the Blaze will stop burning and charge up for another salvo. Then they repeat the attack process. Blazes drop blaze rods upon death.
Blazes drop more XP than similarly sized mobs, and blaze rods are always useful for potions, so they are a hot commodity. Blaze spawners are unique in that they exist in the world naturally, but cannot be manually set by the player, making blaze grinders rare and valuable.
Wither Skeletons
Wither Skeletons are the tall, black version of the regular skeleton, and also run quickly and dish out powerful melee strikes. They only spawn in nether fortresses, and have a rare chance of dropping a wither skeleton head when killed. Unlike regular skeletons, these wither skeletons hold large stone swords that will also poison you with the wither effect when they hit you. These skeletons drop coal, bones and sometimes their sword or skull upon death.
Skeleton spawners built in the nether can spawn wither skeletons as well, making this the ideal dimension to use them in. Wither skeleton skulls are always in high demand, due to withers themselves and their nether stars being so valuable.
End Mobs
The new structures being discovered in 1.12.2 Freedonia also uncovered new mobs.
Shulkers
The common shulkers you see in the End City are purple, but multiple varieties exist in the Shulker Ranch. These shelled mobs shoot out bullets and make those who get hit float around or cause respective effects. Many fears of the long levitation effect making loads of casualties. Killing them may drop shulker shells which can be used to make empty purple shulker boxes, a helpful tool to store items even when the box is broken. Shulker boxes can be coloured with dyes by crafting them with a regular purple shulker box. Other drops vary depending on their colour.
Endermites
Don't pearl around too much, or this small creature resembling the shape of a silverfish attack you with the power from the End. They do not spawn naturally, and only drop a few experience orbs.
Passive Mobs
These are the stupid barnyard friends that constantly manage to kill themselves. When killed, many of these mobs drop meat, which is cooked if they are on fire when they die and raw otherwise. This makes them a good source of food.
Cows
Cows. You already know what they look like. You breed them by using wheat, and they drop leather and beef upon death. You can also use a bucket on them and get the poison-healing/cake ingredient milk.
Automatic pig and cow grinders can be found all across Freedonia, allowing you to stock up on cooked meat when you find them.
Mooshrooms
Mooshrooms, or Mushroom Cows, are like normal cows, but are red and have mushrooms growing on their back, and only spawn in Mushroom Islands. They have everything a regular cow has and more. Similar to buckets and milk, if you use a bowl on them you will get mushroom soup. Shearing these cows will drop their mushrooms and turn them into normal cows.
Sheep
"You kill them, I kill you. Simple." - 
sheep1997
Minecraft sheep are like real sheep, but square. They are usually found with white wool, although they can rarely be black, brown, or even pink. You can use dyes to colour them and use shears on them to get 1-3 blocks of wool. They regrow it by eating grass, and the colour they were most recently dyed will be preserved. Drops wool and mutton upon death. Can be bred using wheat.
When renamed to "jeb_", sheep will cycle their hue like something out of a psychedelic hallucination.
Pigs
Pigs are pink, made of meat, and can be bred with carrots. You can ride them with a saddle for fun, and to play Pigchinko. If lightning strikes a pig in the overworld, it will transform into a zombie pigman, although this is very rare. Pigs drop raw porkchops upon death, or like most passive mobs, the cooked version of that meat when killed by fire.
Chickens
Chickens flutter around and occasionally lay eggs on the ground. Drops feathers and chicken upon death, and can be bred with seeds. Their eggs can be used to spawn more chickens, so one chicken will always be enough to start a farm.
Squids
Squids are the derpy things swimming in the ocean, which always manage to swim out of their water source and suffocate. They can be found in any water source and drop ink sacs and clay balls upon death.
Due to the low spawn rates of squid, and the hassle of both traversing water and diving for fallen ink sacs, ink sacs are unusually valuable. It's always worth harvesting squid when you find an easy opportunity to do so.
Tameable Mobs
"Good Doggy" -
monk30lol
These mobs can become your friends if you give them things.
Wolves/Dogs
Wolves are wild dogs that spawn in packs and are found in taiga biomes. Wolves are normally passive to the player (but not to sheep), but will become aggressive if any nearby wolves are attacked. Wolves can be tamed into dogs by feeding them a random quantity of bones. Dogs will follow their owner, even via teleportation, and will attack any mob that harms them. They can be made to sit, and bred/healed with meat. Wolves do not drop anything upon death.
Ocelots/Cats
Ocelots spawn in jungle biomes. They are fearful of the player and will normally spring away, but can be coaxed into approaching and then tames using raw fish. When tamed, it will change into one of three colours of cats. These cats do not fight and never take fall damage, but they will repel creepers. Drops nothing upon death.
Horses
Added in 1.6, horses spawn naturally in plains and savanna biomes. They can be tamed by riding them or feeding them hay bales, wheat, sugar or apples. They can be ridden with a saddle and given iron, gold or diamond horse armour. Breeding two horses together with golden apples or carrots will make a baby horse with speed, health and jump height similar to the two parent horses. Breeding horses to maximise these characteristics is a must if you want the perfect mount. Horses, donkeys and mules make a horrific scream and drop leather upon death.
Donkeys can also be found naturally. They are rarer, smaller, and overall technically inferior to horses, but they do have a distinctive appearance. They also cannot wear armour, but they can carry chests which will hold items.
Donkeys and Horses can be bred together to get mules, which are almost as healthy, fast, and strong as the parent horse, but can still carry a chest like a donkey. Mules can not be bred.
Zombie and Skeleton horses are extremely rare. Zombie horses can only be found in Delta City legitimately, while skeleton horses can still be found all over Freedonia as a result of the thunderstorm weather in mid-2021 which called an armed horde of skeletons riding on their horses.
As of the time of writing, lag prevents mounts from travelling any faster than a snail's pace and being practical in any way, or even causing them to disappear into the void.
NPC Mobs
These are mobs that look like they might be sentient but are in fact not.
Humans
Humans (aka Steves) were mobs that wandered aimlessly. If any of them were attacked, they would from then on attempt to kill you. 
SlowRiot transformed these into the Steve Police that would hunt down PVPers. But then Notch wrote them out of the game. Pigmen Police had replaced them for many years until the 1.12.2 update when the humanlike Steve Police made a comeback.
Testificates/Villagers
Villagers are passive mobs that spawn in little villages. They have Squidward-esque noses, can open wooden doors to enter their houses during the night, and can offer different trades to the player depending on their profession. Sometimes they "converse" with each other or you by staring straight at you for a bit. Zombies will track down and zombify or kill villagers, and can quickly annihilate all the poor, defenceless saps in a village if left unchecked. If villagers feel their village is depopulated enough, they will breed children that are capable of playing tag until they grow up. They drop nothing upon death.
Villager trades are almost always worthless, except for a few exceptions and unless you need a specific item. Villagers are arguably much more useful for making iron grinders, where their village-forming mechanic is manipulated to continuously spawn in iron golems.
Utility Mobs
These are mobs you can create yourself.
Snow Golems
Snow Golems are pumpkin-headed snowmen made by placing two snow blocks on top of each other and then placing a pumpkin directly on top of it. They throw snowballs at any hostile mob that comes close. Doing this is an act of suicide though, because snow golems only have 2 hearts of health, and can't damage any of the monsters they are provoking. Snow golems also melt and die in warm biomes. Drops snowballs upon death, but not enough to recoup the cost of summoning them.
Snow golems leave a path of snow wherever they go, except in the Nether. This will provide an infinite and rapid source of snow.
Iron Golems
Iron golems look like buff villagers made out of iron, and are made by placing four blocks of iron in a T shape, then placing a pumpkin directly on top of it. Like snow golems, iron golems are hostile to hostile mobs, but rather than throw harmless snowballs, they rush enemies down and launch them into the air with a powerful melee attack. This capability for damage and a tanky one hundred hp makes them excellent guardian mobs who can slay dozens upon hordes of monsters before going down. Iron golems can also spawn naturally in a village with 10 villagers and 21 houses, and these will not hesitate to attack YOU if you hurt a villager. Drops three to five iron ingots and sometimes a poppy upon death.
Iron golems are most commonly ground up for iron in the dozens of iron grinders across Freedonia. Most of these grinders are blocked off by anyone outside their owner and their circle of friends. Owning an iron grinder is a valuable status symbol, because not only do they provide a constant source of income, they are expensive and time-consuming to construct.
Boss Mobs
These are mobs that are considered bosses.
The Ender Dragon
The Ender Dragon was the first boss mob implemented into Minecraft. This boss is extremely hard to kill and it usually takes a team of well-prepared players or one skilled individual to defeat this mob, as it has high damage, extremely high hp, and spawns in an arena that can heal it. The Ender Dragon is located in the End dimension, which you can ordinarily only reach by finding End portals in strongholds. However, in Freedonia, natural strongholds and their End portals long did not exist until 1.12.2 when the world expanded with strongholds being generated for players to explore. Admin-made End portals do exist, however, they are somewhat difficult to find. The original Ender Dragon was slain long ago, with not much-known information. The fate of the original dragon egg is currently unknown, though there are extremely few others known to exist.
The update to 1.12.2 newly introduced a method to call out the Ender Dragon to fight again using End Crystals which were added in Minecraft 1.9. The dragon’s HP is shown up on the HUD while she is awake. Upon death, the dragon drops many XP orbs, a dragon egg and an elytra, and a portal back to the Normal world.
Withers
This mob can be summoned by any player by placing 4 soul sand in a T shape, then placing 3 wither skulls on top of the soul sand. The wither is capable of flight, is very fast, and deals an immense amount of damage using a few different attacks. These attacks are firing slow blue skulls randomly, fast salvos of black skulls that inflict a withering toxin, exploding violently when spawned, and breaking surrounding blocks when trapped, though in Freedonia this is disabled. It also regenerates health, and after losing half of it, it will activate a shield which deflects arrows. Upon death, the Wither has a high chance of dropping a nether star, which can be crafted into a beacon or an end crystal.
There are a number of places in Freedonia where withers can be safely farmed by spawning them in a cage where they cannot escape. Withers, like all mobs, are crippled by the lag and are thus much easier to kill than normal. Spawning a wither creates a spooky noise that plays for every player in that dimension, just like lightning. Withers have an HP bar that shows up on the HUD when a player is near them, and named withers trapped underground can be used to create messages.
Giants
Giants are massive zombies that can deal a ton of damage. They are, however, broken and unfinished. Giants cannot move properly, and can only be spawned by admins. It was extinct, to say the least, until the server dungeon revived the old prototype into a crushable, terrifying beast which cannot be attacked by melee weapons whatsoever.