Lifecaster

Alongside your spell slots, as a free action, you also use some of your health to cast your spells. However, the neat part is that your used health boost your spell's power.

If casting a spell that does not require the roll of a die for healing or damage, you (the caster) must also make a CON saving throw (DC = 15 + CON): on a success, you take half the damage from your Life Caster Die (round up), and the spell casted does not expend a spell slot. On a failed save: the spell is casted normally, however, you must take the maximum damage from your Life Caster die. 

Note: the damage taken from your Life Caster Die cannot be reduced in any way.

Every 4 levels upgrade your dice; {lvl.4: 1d6 / lvl.8: 1d8 / lvl.12: 1d10 / lvl.16: 1d12}

Mastery over your own blood and soul has strengthened your body. (+1d10 to Hit point total)