Asmodeus's Last Resort

This box of 12 bullets refills every dawn and any unused ammunition vanishes as the box refills. It is full of hellfire ammunition that deals an additional 1d8 Fire and 1d8 Necrotic Damage. Anything Killed with this ammunition has it's soul sent directly to the armies of Asmodeus. Everyday the owner of this box must beat a DC 20 Wisdom saving throw, otherwise they are compelled to use this ammo with every attack as their only method of attack until they run out of ammo. Regardless of if they are currently charmed or not, if the wielder of this ammo box only has one bullet remaining from this box upon falling to 0 hp, the immediately use their reaction to use the last bullet to prevent their enemy from getting the kill by taking it themself.