Skeleton Castle
Skeleton Castles are castles that are randomly spawned. They are usually found in plains biomes. There are several different types and forms.These castles have chests with items and skeletons gaurding them. They are often generated with a sewer system below, some sewer systems can grant access into the heart of the castle from the outside.
Be warned, a necromancer is usually somewhere inside of these.
Known Skeletons
The Skeletons inside these castles spawn with a large amount of different armor and weapons.
Defender Skeletons are skeletons that spawn with a sword and shield. They are usually in iron or gold armor, and they walk slowly as they are constantly blocking. In a fight, ignore these and focus on more high profile skeletons.
Mage Skeletons are skeletons that spawn with staffs and usually with iron or leather armor, and they can cast spells at you or even heal fellow skeletons. They should be the first skeleton you kill.
Normal Skeletons spawn with chain-diamond armor and usually just have a sword. These are the most common type of skeletons.
Skeleton Archers spawn with iron-diamond armour and an un-enchanted bow. They don't shoot very quickly, and are much more innacurate than normal skeletons.
Grenadier Skeletons usually spawn with chain armour, and a wood or stone sword. They are mainly support units, and are capable of throwing grenades. These work like splash potions, but can be thrown farther and can have multiple effects on them at once. Some effects are harmless, like Water Breathing. But some effects can debuff or harm you, like Slowness or Poison.
Necromancers
Necromancers are a powerful mob found in the castles that boast 60 hearts of health. Necromancers have a few magical abilities, including a life drain (taking health from the player to recover it's own health), and spawning a mob called "Summoned Undead", which is a melee fighting skeleton that attacks you. They can spawn the Summoned Undead very rapidly, and they tank hits for the necromancer. When you do manage to kill the necromancer, he drops a Cursed Bone. Do not attempt to fight the necromancer unless you are confident with your skills, and are very well geared, as the necromancer has three times the health you do, and will have the Skeletons and Summoned Undead defending him.