Role-playing Games Stack Exchange is a question and answer site for gamemasters and players of tabletop, paper-and-pencil role-playing games. It only takes a minute to sign up.
Sign up to join this community
The description of Luck Blade (DMG p179) says:
Luck. If the sword is on your person, you can call on its luck (no action required) to reroll one Attack roll, ability check, or saving throw you dislike. You must use the second roll. This property can’t be used again until the next dawn.
Do you have to be attuned to it to receive the benefit, or as the description says, is having it on your person enough?
The rules for attunement state:
Without becoming attuned to an item that requires attunement, a creature gains only its nonmagical benefits, unless its description states otherwise.
The description does not say it works while unattuned, so you must be attuned. As an example of a weapon that grants a bonus without attunement, consider the Hazirawn:
Even if you aren’t attuned to the sword, you gain a +1 bonus on attack rolls and damage rolls made with this weapon. If you aren't attuned to Hazirawn, you deal an extra 1d6 necrotic damage when you hit with the weapon.
-Hoard of the Dragon Queen
