O is for Osteomancer

The Osteomancer is a 3rd era prestige class that appeared in the March 2004 issue of Dragon Magazine. While the idea of a bone mage seems like necromany it's actually a specialized version of transmutation magic. These hearty mages manipulate there core (as they call their skeletons). They can extend and retract bone spurs to create armor or natural weapons.  I never got to play one, but I always loved the idea. It reminded me of Spyke and Marrow from the X-Men.

(insert juvenile quote about boners) because O is for Osteomancer...

Osteomancer by Pyridoxine 

Jack the Osteomancer

The capricious wizard, Jack is a practitioner of the rare school of magic known as Osteomancy. A student of Raid's father, Jack is anything but your typical spellslinger. He travels the world and seeking new transmutation spells. While most view the arcane arts as a mental pursuit, to Jack sees it as a way to hone his body. Jack has been known to teach his unique style of magic to those he deems worthy.

His ultimate goal is to find learn the rarest of osteomancy spells, rumored to allow the caster to telepathically control the skeletons of others.

Boneless
1st Level Magic-User and Elf Spell
Range: 0
Duration 6 turns
This spell allows the caster to dissolve his bones (which reform after the spell is over). His move becomes 10' (3'), but he can now squeeze through any surface that has at least a diameter of 8 inches. Casting the spell puts quite a bit of strain on the caster and he takes 1 point of Constitution damage (which is healed when takes 8 hours of rest).

Bone Spur
2nd Level Magic-User and Elf Spell
Range 0
Duration: 12 turns

This spell allows the caster to extend his bones out of his hands/feet to create natural weapons. These weapons are considered magical for the purposes of damaging creatures. Casting the spell puts quite a bit of strain on the caster and he takes 1 point of Constitution damage (which is healed when takes 8 hours of rest).

Armored Core
2nd Level Magic-User and Elf Spell
Range: 0
Duration: 6 Turns

This spell allows the caster to turn his skeleton (or core) into armor. During the spells duration the caster is assumed to have an Armor Class of 6 (though this doesn't affect his spell-casting). Casting the spell puts quite a bit of strain on the caster and he takes 1 point of Constitution damage (which is healed when takes 8 hours of rest).

Knit the the Flesh and Set the Bone
3rd Level Magic-User and Elf Spell
Range: 0
Duration: Permanent

This spell is the same as the first level cleric spell Cure Light Wounds. This also heals constitution damage caused by Osteomancy spells (such as Bone Spur).