Wither Skeleton

Wither Skeletons are dangerous hostile mobs that spawn in Nether Fortresses. Wither Skeletons are the Nether equivalent of skeletons. Unlike skeletons, however, Wither Skeletons use stone swords and are over two blocks tall. When hit by a Wither Skeleton on any difficulty, the player is inflicted with the "Wither" effect for 10 seconds, darkening the health bar and further damaging the player. When killed, the mob may drop coaland bones, and very rarely drop their skull and the stone sword. The skulls are the key items to creating the Wither boss.
Wither Skeletons, like all Nether mobs, are immune to fire and lava and are not damaged by daylight. Some Wither Skeletons can also pick up items, weapons, tools, and armor, similar to other undead-type monsters.

Spawning

Wither Skeletons only naturally spawn in nether fortresses (even if the area where a fortress would be was generated before their inclusion, since it is tied to the location of the fortress, not the fortress itself). Block type does not matter with naturally spawned Wither Skeletons (e.g., replacing a Nether Fortress' bricks with normal blocks will still allow wither skeletons to spawn); they follow the same spawning conditions as naturally spawning Skeletons: light level 7 or less where their lower half will be.
When used in the Nether, Skeleton spawn eggs are able to spawn Wither Skeletons instead of the normal skeletons 80% of the time. Similarly, when a spider is spawned in the Nether (whether via spawn egg or a mob spawner), it has a slight chance of spawning with a wither skeleton jockey instead of an ordinary skeleton.

Combat

Wither Skeletons are tough mobs to fight due to their high attack strength, and because they inflict Wither, as well as they are likely to coexist with a Blaze. Their biggest weakness is that they can't pass through a two block high passage, because they are too tall, much like Endermen.
If there are lots of Wither Skeletons and Blazes around, bring some Blocks of Iron and a pumpkinto make an Iron Golem. This is also a good way to farm the drops of the Wither Skeleton.
If an Iron Golem is not an option it is advised that the player treat the Wither skeleton as they would a creeper, albeit with far more care. If you attack and move backwards at the same time you should not have any trouble avoiding damage provided you have some room to maneuver. If you have your back to a wall spam attacking should be enough to kill a single Wither Skeleton without taking damage. If you have your back to a wall and are facing more than one Wither Skeleton it is strongly advised that you move to a position where you have room to maneuver as the Wither Skeletons move slightly faster than zombies and so more easily overwhelm you. Sniping with a bow is also effective although it is not recommended at under 10 blocks away (without a punchenchantment) as Wither Skeletons move surprisingly fast.
If you find yourself facing a Blaze at the same time the best course of action is to move into a place inaccessible for the blaze -such as a corridor- and then proceed in taking the above steps to kill the Wither Skeleton. If this is not possible it is suggested that the player run out of range of the blaze and turn to face the Wither skeleton. It is strongly advised that inexperienced players do not face both mobs at the same time as this often leads to death, but for more experienced players willing to face both you should either; deal with the blaze first by charging at it with a sword (do not use a bow as you will be exposed to attack) and then turning and facing the Wither Skeleton or (more recommended) putting the Wither Skeleton between yourself and the Blaze so as to use its body as a shield against the Blaze's fireball attack, and then charging the Blaze once it is dead.
Like all mobs, Wither Skeletons can travel through a Nether Portal. This means that if you put a Nether Portal inside the Nether Fortress, and yourself between the portal and a Wither Skeleton (or any other hostile mob), the Wither Skeleton will travel towards you but teleport into the overworld. This means that once you get back from the Nether you might still be up for a fight against a Wither Skeleton.
It is also possible to use an invisibility potion therefore be able to fight the Wither skeleton with only stone sword and no armor. This is one of the easier ways to kill a wither Skeleton but it requires you have a Invisibility potion.

Witch

Witches are hostile, ranged mobs commonly spawning in Witch Huts. They're the second hostile ranged mob to spawn in the Overworld - the first being the skeleton.

Appearance

Witches have a similar appearance to the villager mob, and they wear purple and green robes with brown leggings underneath. They have large noses (which moves slowly around on the Witch's face, as stated in Dinnerbone's tweet) with a single wart and have lavender colored eyes. They wear the usual witch hat with a green buckle on it, and their skin is slightly paler than the normal villager. However, witches periodically give off purple star particles similar to the villager's green stars.

Combat

The witch mob uses splash potions of poison, weakness, damage, and slowness to fight the player. The current order of potions thrown is; slowness, poison, they will then proceed to throw potions of harming until the player is no longer poisoned which they will rectify by throwing another splash potion of poison and will continue to do this. The splash potion of harming will occasionally be substituted by potions of slowness. These potions will affect other mobs - not just the player. The witch does not burn in sunlight and when set on fire, drinks a potion of fire resistance. This can be seen when a bottle appears in the witch's hands. Iron Golems will attack witches as most other hostile mobs.
Witches are almost immune (85% damage resistance) to splash potions of poison and instant damage. When damaged, they will drink a potion of healing, healing themselves. When drinking a potion, a witch's nose will point straight forward (instead of down). While healing they can't attack the player. If lit on fire by lava or fire, witches will quickly drink potions of fire resistance, making lava and fire ineffective ways of killing witches.
A bow will likely be the best weapon for dealing with a witch, as the splash potions have only a short range (at most nine blocks) compared to arrows (which, when fired straight at full charge, travel 24 blocks). If a bow is not an option, however, a direct melee charge is the best option. Due to the witch's slow attack speed, if the player runs in a straight line and manages to get a quick sword strike in, the witch will try to heal themselves with a potion of healing, leaving the player to attack them without fear of retaliation.

Mooshroom

     

Appearance

Mooshrooms use the same model as the cow, but have red skin (with the white patches also used by the cows), black eyes, and are covered with red mushroom growths.

Uses

Mooshrooms can be sheared for 5 red mushrooms, which turns them into cows. Sheared Mooshrooms cannot be reverted back to Mooshrooms. If killed, they drop leather and raw beef (steak if killed with fire), exactly like cows. Mooshrooms can be milked with a bucket as well, but also can be "milked" with an empty bowl to obtain a bowl of mushroom stew, making them very useful.

Breeding

Breeding a pair of Mooshrooms will produce another Mooshroom. If you shear the baby Mooshroom�s parents, the parents stop following the baby.
Baby Mooshrooms will walk faster and are followed by their parents. They will not drop anything when killed, but still can be milked and sheared. Shearing will turn the baby Mooshrooms into Calves.