2. Have it deal X Vile damage on a failed will save, if that damage is enough to kill the player, their soul is absorbed instead. Otherwise, they must try the spell again. Then make it only reversible by wish, miracle, reality revision, etc.
3. Will save. The effect on the soul outweighs the effect on the body I think.
5. Soul Rape
Vile Damage: This type of damage represents such an extreme corruption that it does not heal normally, and can only magically be healed in the are of a Consecrate spell. (Is it Consecrate? I forget.)
"Your soul will be inside me... whether you like it or not!"
Sounds like a perverted form of violating ones soul to me. Rape fits the bill.