This mod is given at the penultimate mission of The Sacrifice, automatically ranked to level 5.
Umbral Vitality is essentially the Vitality mod with Legendary rarity. It is considered the same mod as its Common counterpart, and thus both mods cannot be equipped together.
The set bonus for Umbral Vitality increases the maximum health given by the mod by 25% of mod's value when using 2 set pieces and 75% when using 3. At max rank with full set bonus, Umbral Vitality grants a health increase of 770%, and increases Sentient damage resistance by 19.25%.
Resistance values in the above stat table are calculated based on set bonus values, displayed values are rounded to the first decimal place ingame.
This mod outperforms Vitality from rank 8 when using 2 set pieces and from rank 6 when using 3 set pieces.