A guild of cunning thieves sneaks their way into an opulent mansion, filled with the riches that only generations of power can acquire. The mansion's private guard patrol within, seeking out intruders and relentlessly hunting down those that their efforts reveal. Every shadow is a potential hiding spot, every noise might be a clue to the presence of thieves. Every second lost can mean the difference between victory and defeat.
This is the stealth effect used in Nightblade. A thief in shadow becomes translucent, and ultimately transparent when in the darkest shadows.
oooh...is it a magic/potion/ability thing? Can you grab someone while in stealth and perform a shadow kill?
Stealth in shadows is a permanent ability of thieves, with the amount of stealth varying by the darkness of the shadow. This ability is only disrupted when they take damage. Thieves can knockout a guard from behind with their Blackjack, but this isn't linked to their stealth level in any way at the moment.