Soul Engine

15th-Level Artificer Feature

You can fashion and attach a Soul Engine anywhere to your Bone Armor. By imprisoning the souls of the fallen in the Soul Engine, you can fuel your Necrotic Sacrifice features without using your own life essence.
Using your Smith's Tools you can perform a hour long process to fashion and attach a Soul Engine to your Bone Armor. To perform this activity, you need a diamond worth 1000gp and a heart or brain which are both consumed in the process. The Soul Engine requires attunement to use it's features.
The Soul Engine has the following features:

The Soul Engine has 4 charges.
When you roll a sacrificial die you can expend 1 charge to ignore any damage you would take from it.
When you roll a sacrificial die, once during your turn, you can expend 1 charge to add another 1d6 to that roll.
As a reaction immediately after a creature dies within 30 feet of you, you can have that creature make a Wisdom saving throw against your Spellcasting DC. On a failed save you capture it's soul within the Soul Engine and it regains 1 charge. You can not capture more souls if the Soul Engine has it's maximum charges.