Blooded weapon
weapon, uncommon
The sahuagin, the creators of these weapons, are known for their cruelty and sadism, but none so much on display as during the forging of these weapons. Forged during dark rites involving the torture and slow death of prisoners, blooded weapons provide a +1, +2, or +3 bonus (depending on the level/CR of the prisoner being sacrificed) that is magical for all intents and purposes, but does not give off magical aura under a detect magic unless opposed by a caster's attribute check against DC 20. It will, however, glow fiercely red when any alignment-detection magic is used around it.
The weapon does not require attunement to use. Note that these weapons always have a loop at the end of their shaft, to which sahuagin attach rope, allowing them to recover the weapon (using a bonus action) when thrown.
Curse: Sahuagin Cruelty. If a character of good alignment uses this weapon for more than 7 days, they must begin Wisdom saving throws (DC 15) on each long rest. During the long rest, the character hears whispers of anguish and pain during their dreams or trance, with the bad dreams increasing in intensity with each successive failed saving throw (once, whispers; twice, the screams are disturbing). If they fail the saving throw three times in a row, they polymorph permanently into a sahuagin (something only a greater restoration or wish spell can undo) and immediately move to the nearest large body of water in order to join a sahuagin tribe. If the character makes a saving throw before reaching three successive failures, the count resets to 0.
If the character is using both a blooded weapon and blooded armor, the Wisdom saves are at disadvantage.
Before the transformation, the curse may be lifted by a remove curse. The character will be loathe to part with the weapon for any reason; the character must make a Wisdom/DC15 save at the time, and if they take a long rest without it, they must make a Wisdom/DC 15 save, with failure indicating they suffer one level of exhaustion and are agitated to reunite with the weapon as quickly as possible, openly threatening or attacking those in their way if necessary, though they will not risk their own life to do so. If the character can go seven days without being in the weapon's presence, the curse is broken.
Anyone seeing the weapon can make a History/DC15 check to know the legends surrounding these weapons; having any sort of mariner or sailor background provides advantage on the check. Success yields the knowledge, "Legends tell that any weapon of the "sea devils" must immediately be cast back into the ocean, lest they curse those who carry them."