This side-quest is simlar to the quest to donate to the Temple of Light, but in this case instead of money you will be offering blood sacrifices… Aren’t you kind? To do this, you simply go into a town and get villagers to like you. Use the follow expression to get them to follow you and fast travel back to the Temple of Shadows. Enter the temple and use the lever next to the Wheel of Misfortune to complete a sacrifice.
You will earn shadow points for every sacrifice you make and depending on the manner of execution and the number of sacrifices at once the number of points you accrue will vary. Note that for every sacrifice you make, you will earn +50 evil morality points.
After you have accrued enough shadow points (2000), you will be able to perform the ultimate sacrifice for a special legendary weapon. To do this, make sure you get married and then bring your wife/husband to the temple and sacrifice them between 12am - 1am (you can track the current time on the menu screen).