The "Acrobatics" and "Shadowrunner" perks unlock the ability "One With the Shadows" Rank I and II, respectively. These increase damage dealt to enemies, but makes it easier for enemies to detect you.
If you are not invisible, you must be within 48 feet of the enemy. If you are invisible, you must be within 24 feet.
Damage mult is 1.5x for Rank I and 2.0x for Rank II.
The effect lasts 60 seconds.