Comments from the Thumb: As a joint effort between the Finger and Thumb, we present to you our take on the Osteomancer PrC of 3.5e. Originally a straightforward and uninspired archetype that didn't add much backbone to the class, the Finger has reworked the skeleton of our build using a new mechanic: hit dice as pseudo-spell slots. Now you have to keep track of how many times you use your abilities, because if you run out of hit dice in combat, you're boned in terms of self-healing. Something something something, bone puns.
Comment from the Finger: Yes Thumb, that was very humerus. You have quite the funnybone.
The legendary Bone Knights are warrior-mages of an ancient and secretive cult of transmuters. Called by some the Osteomancers, it is said that these soldiers have the hideous and disfiguring ability to control their bones in entirety, using them for weapons and armor, and even change their size or shape.
Starting when you select this archetype at 3rd level, you gain the ability to sprout or retract plates of bone from your skin, granting you an Armor Class of 14 + your Dexterity modifier. You cannot wear armor while you have an exoskeleton. The sudden restructuring of your skeleton takes 1 minute to occur, during which you cannot move or take any actions.
At 3rd level, you regain your total number of hit dice when you finish a long rest.
At 7th level, your exoskeleton has spiny protrusions of bone which can pierce your enemies. As a reaction when you take damage from a melee attack, you can expend a Hit Die to fire these spurs at your enemy. The creature that damaged you must make a Dexterity saving throw (DC equal to 8 + your Constitution modifier + your proficiency bonus) or take piercing damage equal to the number rolled on the Hit Die + your Constitution modifier.
At 15th level, the damage increases to twice the number rolled.
Starting at 7th level, you can sprout an agonizing blade of jagged bone from both of your wrists as a normal creature would draw a weapon. Retracting them is a bonus action. Your bone blades are light, finesse weapons that can't be disarmed and deal 1d8 piercing or slashing damage on a hit (your choice when you create the blades.) You are proficient with these weapons. Your bone blades count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.
When you deal damage to a creature with your bone blades, the wound bleeds profusely, dealing an additional 1d4 slashing damage for each hit at the beginning of the creature's next turn.
At 10th level, you learn a more fine control over your bone structure. You may expend a Hit Die to cast enlarge/reduce or alter self (to use only the Change Appearance option), targeting only yourself and requiring no spell slots, spell components, or concentration.
Starting at 15th level, your blades can cause a malaise to settle into the core of a creature's bones. You can expend a Hit Die to deal additional necrotic damage equal to the number rolled on the Hit Die + your Constitution modifier on your next attack made with a bone blade.
At 18th level, your bones have become as hard and durable as metal. Bludgeoning, piercing, and slashing damage that you take from nonmagical weapons is reduced by 3.
In addition, as a reaction when you take damage, you may expend a number of Hit Dice to reduce the damage taken by an amount equal to the Hit Dice + your Constitution modifier for each die rolled
Changelog: 8/14/15: Exoskeleton: Inconsistency clarified - sprouting or retracting plates takes 1 minute. Also, you cannot wear armor with an Exoekeleton.
Bone Blade: Bleeding damage clarified to 1d4 per each hit at the beginning of the target's next turn.
8/15/15: Skeletal Shift uses alter self rather than disguise self.
Adamantine Bones: Additional effect added: Expend and number of HD to reduce damage by HD + Con (Thank you, Kyle Dawson!)
8/25/15: Bone Blades: Producing Bone Blades takes as much time as drawing a weapon, and retracting them takes a bonus action.
9/9/15: Sap Life: Changed the duration from "rest of your turn" to "on the next attack".
8/18/16: Bone Blades: 1d8 damage, count as magical