The Armored Bones are various types of Skeleton monsters that spawn in different areas of the Dungeon after Plantera is defeated. You are alerted to the new spawns with the message "Screams are echoing from the dungeon..." There are three different "factions" of Armored Bones: Blue Armored Bones, Hell Armored Bones, and Rusty Armoured Bones. All Armored Bones have (informally named) four different types of monsters. All may drop the Wisp in a Bottle, Bone Feather, Keybrand and/or Magnet Sphere.
Blue Armored Bones
The Blue Armored Bones spawn in parts of the Dungeon with a Brick wall, and are accompanied by Skeleton Commandos, Necromancers and the dangerous Paladin miniboss. There are four variants, each with different appearances, health, damage and defense. They may drop Armor Polish in addition to the standard Armored Bones drops.
Hell Armored Bones
The Hell Armored Bones spawn in the lower third of the dungeon (approximately) with a Tiled wall. They spawn along with Tactical Skeletons and Diabolists. They inflict the On Fire! debuff. Their area has the Molten Legion Flag in it.
Rusty Armored Bones
Rusty Armored Bones spawn only in the parts of the Dungeon with Slab walls, along with Skeleton Snipers and Ragged Casters. Like the other Hard Mode Dungeon Bones, they have four different versions with unique looks and stats. They inflict the Bleeding debuff. They spawn in the area of the Dungeon with Rusted Company Standards. They may drop the Adhesive Bandage (like all monsters that may inflict Bleeding) in addition to the standard Armored Bones drops.