Harold is crossbow capable of instilling doom effect in the bolts it fires.
Acquisition[]
In the Den of Thieves side quest during Chapter Ten – Allied Siege Camp of 
Baldur's Gate:
Siege of Dragonspear (2016)
This icon indicates content from the Siege of Dragonspear campaign of the Baldur's Gate: Enhanced Edition., you'll meet Rhynwis, make a treaty between her shadow thieves and the coalition camp then demand a share of profits. She'll reveal a hidden cache location (4047, 1056) in the Underground River entrance where you'll find the crossbow alongside with 527 
plus some random gems.
Description[]
| “ | When Fitzallus the Footpad, a Sembian bard, had this heavy crossbow commissioned, he talked endlessly about how incredible the weapon would be. His friends teased him that the crossbow was his new "best friend" and that he should name it. Finally, the crossbow was ready, and Fitzallus strode into the tavern with the gleaming weapon and proudly introduced it as "Harold." Fitzallus died during a burglary several months later, and though his will specified he be buried with Harold, the crossbow vanished before the ceremony. | ” |