Resurrection of creatures.

Thank you very much. And is it possible to increase the amount of dark energy, and generally, how much of it is there?

Actually, when playing as a Necromancer, the bar showing the level of dark energy is always right in front of you. That is, in plain sight. It's located near the top of the screen. You can increase dark energy in several ways: by developing the Necromancy skill, by collecting artifacts from the Necromancer set, and by building specialized buildings in the city.