This mod is given at the penultimate mission of The Sacrifice, automatically ranked to level 5.
Umbral Intensify is essentially the Intensify mod with Legendary rarity and 5 more ranks. It is considered the same mod as its Rare counterpart, and thus both mods cannot be equipped together.
The set bonus for Umbral Intensify increases the Ability Strength given by the mod by 25% of mod's value per set piece equipped, while the other two pieces gain an additional 25% with the full set for a total of +75% of their values. At max rank with full set bonus, Umbral Intensify grants an Ability Strength increase of 66%, and increases Sentient damage resistance by 16.5%.
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 Intensify from rank 7 alone, from rank 6 with 2 set pieces and from rank 5 with 3.
Umbra mods have a unique polarity, whose matching polarity can currently only be found on Excalibur Umbra, Exalted Umbra Blade, and the Skiajati. It is not possible to (re-)add an polarity to a mod slot, so it's advised not to overwrite a pre-existing one.