The sword is said to contain the soul of a being that had crossed Clavicus Vile.
Until the "Clavicus Vile's Shrine" quest has been completed, the sword will remain as a quest item with zero weight. The shrine quest requires the Hero to obtain the sword and return it to Clavicus Vile, in which case, the Hero will receive the Clavicus Vile's Masque as a reward, which boosts Personality by 20 points. Otherwise, the sword can be kept and thus end the quest.
- Even though it can be kept as the reward of a Daedric quest, it is not considered a Daedric artifact.
- Umbra becomes especially powerful when used with Azura's Star, as an easy way to recharge it.
- It has the highest base damage of any one-handed weapon, and the highest base damage of all non-conjured Blade weapons in Oblivion and all of its plug-ins. The Perfect Amber Hammer added in Shivering Isles is the only non-enchanted, non-conjured weapon with a higher base damage (29).
- With a Blade skill of 100, a Strength of 100, and 125% condition (requires an Armorer skill of 75), it can reach 33.
- Umbra is one of the few swords in Oblivion that doesn't have a sheath.
- While a quest item, Umbra is weightless.
- Umbra is the scientific name for the darkest part of a shadow; in particular, the shadow cast by the Moon that completely blocks out the Sun during a solar eclipse. It comes from Latin, where it means "ghost" or "shadow."
- If acquired with console commands, Umbra will be classified as a quest item and therefore can't be removed.
- It can be a part of a deadly combination if used with Goldbrand, since it has the Soul Trap enchantment that can be used to have Goldbrand constantly charged.
- Barbas's warning about giving Umbra to Clavicus Vile turned out to be true: forty years later the Umbra spirit attacked Clavicus and fled from his realm, powering the Infernal City of Umbriel which went on a path of destruction in Tamriel, namely destroying Gideon, Stormhold, and Lilmoth in Black Marsh, parts of Morrowind, and Cheydinhal in Cyrodiil 
This section contains bugs related to Umbra Sword (Oblivion). Before adding a bug to this list, consider the following:
- Umbra can be added to the inventory with zero weight but it cannot be removed. For this to occur, tell Umbra during the Daedric quest that the Hero will leave peacefully, then after the quest update to return to the shrine has popped up, kill Umbra but do not take anything. Head back to the shrine and refuse to give him the sword. Go back to Umbra and take all of her armor and Umbra's sword. The sword now weighs nothing and cannot be dropped. Also, if the sword is obtained before the quest has started, the same will happen, the quest can be done later.
- The sword can be used for easy jailbreak. For this bug, the sword must be a quest item. When in jail, all items are removed, but Umbra can be used even when it has been taken. Place the sword in a hotkey slot. When making the escape, hit the hotkey and Umbra will equip.