Sacrificial Pit (Warcraft III)

The sacrificial pits of Azjol-Nerub were used long ago to sacrifice enemy forces in exchange for success in battle. They are now used by acolytes of the Scourge who wish to serve as the eyes and ears of Ner'zhul, allowing them to shed their bodies and take on the forms of invisible shades. Shades are detectable only by magic, making them excellent spies.

Abilities

 * [[File:BTNSacrifice.png]] Sacrifice - 1 - Target an Acolyte to sacrifice it and turn it into a Shade. Shades are invisible spirits that can see invisible units. Shades cannot attack.

Pit of Fiends
Being a nerubian pit full of bones, the Pit of Fiends might be a sacrificial pit, though it has nothing to do with shades.