Hellforged Sword (5e Equipment)
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Weapon (any sword), very rare (requires attunement)
While you are attuned to this sword and carrying it on your person (whether you are wielding it or not) you can understand and speak Infernal.
You can use a bonus action to speak this magic sword's command word, causing the flames of hell to erupt from the blade. These flames shed bright light in a 60‑foot radius and dim light for an additional 60 feet. While the sword is ablaze, it deals an extra 2d6 fire and 2d6 necrotic damage to any target it hits, and once on your turn you can can banish (DC 17) a creature you hit with the sword to a random plane of hell.
The flames last until you use a bonus action to speak the command word again or until you drop or sheathe the sword.
Curse. A hellforged sword is linked to a pit fiend or more powerful fiend, and it is used as a trap to enslave foolish mortals. At the hour of midnight of each day you are attuned to the sword, you must make a DC 20 Wisdom saving throw or be affected by a geas spell (9th-level version). The fiend is treated as the caster of the spell. While you are geased, the fiend can sense what you sense, even across planes, and it has a telepathic bond with you. This version of the geas spell allows the fiend to issue suicidal commands - and the fiend in question often does, if it believes the wielder of the hellforged sword is not useful for its purposes.