The Shadow Weave

Channeling the dark space between the Weave of Magic the character can empower Arcane Spells by sacrificing their essence.

You can sacrifice your HP to power your spell casting.  Use your HP as a spell slot to cast an Arcane Spell that is known to you.

You will take your (Character level) x (The Spell Level) + (The spell Level) in Damage to cast the spell.

If this damage takes you to or below half health.  Or if you are under half health and take this damage. You will take a point of exhaustion.