Necrotic Reserve

Each day that you slake your hunger by draining or damaging a living creature's ability score, or draining a living creature's life force, you gain a necrotic reserve.

On days when you have created a reserve, you are weakened but not destroyed when you are dealt enough damage to reduce your hit points to 0 or lower, even if the total exceeds the threshold needed to kill you instantly. (Similar to the effects of the Death Ward spell.)

While weakened and acting on the strength of your necrotic reserve, you may choose to move or take a standard action each round (but not both, nor can you take full-round actions). Additionally, you must still make death saving throws, with any damage taken causing failures. (As per the norm with death saves.)

You move at half speed. Taking movement doesn't risk further injury, but performing any standard action (or any other action the DM deems strenuous) expends your necrotic reserve. If you haven't restored your hit points, and have three (or more) failed death saving throws, you are destroyed instantly.  

As you are weakened in this state, taking any damage after two or more death saving throw failures will cause you to be destroyed instantly, along with any of the equipment you're carrying. (Magical items are exempt from this effect.) 

You may only rely on a necrotic reserve once per day, even if you engage in an additional feeding following a successful return to positive HP.