Altar of Shadows/1.03.24

Undead
As you would probably have guessed, the Altar of Shadows allows Wraiths to morph into Shadows. This time there aren't any unit specific researches to be had, but instead racial mana regen bonuses. The Altar of Shadows has a remarkable amount of hit points, especially considering that it's still a rather small building. But otherwise, it's treated the same as the Barrow and Cage.