The magic that hums in your veins has given you more conviction than sense, but who wants to live forever?

Once per turn, you can invest your vital essence into a spell, making your will more difficult to dismiss. The spell must be one which targets a single creature and requires a saving throw. When the target rolls its saving throw against the spell, you can spend one of your Hit Dice. If you do, you do not regain any hit points; instead, you roll the Hit Die and subtract the number rolled from the target's saving throw result, potentially causing the target to fail the saving throw. If the target still succeeds on its saving throw despite this effect, you gain temporary hit points equal to the number rolled on the Hit Die.

Beginning at 10th level, you can use this effect on a spell that targets all enemies in a given area, such as a cone or a line. The spell must still require a saving throw. When you use this ability in this way, you roll a single Hit Die one time and subtract the result from the saving throw results of all creatures effected by the spell. You also gain temporary hit points equal to the number rolled on the Hit Die regardless of how many targets succeed or fail their saving throws.