Flasher Master Bruiser Mate

Flasher Master Bruiser Mates are a special type of ammunition for Jan Jansen's crossbow, the Flasher Launcher. Unlike most crossbow ammunition, instead of bolts they take the form of skulls filled with a special powder that is capable of stunning an opponent in addition to dealing damage. These bolts appear in Baldur's Gate II: Shadows of Amn and Baldur's Gate II: Enhanced Edition.

In-game description
"This is the ammunition for Jan's crossbow (the Flasher Master Bruiser). These skulls are filled with a special powder that does a little bit of damage and has a chance to stun an opponent (saving throw vs. spells or be stunned for 2 rounds)."