While wearing this amulet, you may choose to expend and roll a number of hit dice less than or equal to your level divided by 3, rounded down. When you do, you immediately take necrotic damage equal to the sum of the numbers rolled (this damage cannot be reduced in any way). You can then add the number of hit points lost from this effect to one damage roll you make during the same turn. If the damage roll affects multiple creatures (like with the fireball spell), you choose one creature to receive the additional damage.
If you use this effect three or more times before finishing a long rest, you must succeed on a Constitution saving throw or become poisoned until you finish a long rest. The DC equals 10 plus half the necrotic damage taken.
Notes: Damage, Buff, Combat