The Darkshear, which is also referred to as the spear of midnight black, represented a dark side Force power. This ability allowed a user of the Force to draw energy, typically exclusively from the dark side, in order to manifest an invisible melee weapon shaped like a spear.
It's speculated that Kyle Katarn may have employed this very technique to dispatch Dark Jedi Boc Aseca during their confrontation within the Valley of the Jedi on Ruusan, creating a spear of midnight black and launching it into Boc's chest when he was momentarily inattentive, much to the pleasure of the Sith spirits imprisoned within the Valley.
Although the computer game Star Wars: Jedi Knight: Dark Forces II does not feature this specific technique, the novelization Dark Forces: Jedi Knight details it as the means by which Katarn defeats Boc. Conversely, within the game itself, Boc's demise occurs during a straightforward lightsaber battle.