Birth: Generate a creature of your mark with Hp equal to your Hp/10. This creature is tied to your life points.
Tied to your life points = when you are healed, it is healed for the same amount /10. If it is damaged, you are damaged for the same amount. Not *10, because that would be an easy target to get to your HP.
It is assumed that rewinding gives you the spell, not the creature.
Untargetable? Perhaps.
Well, what do yah think?