So it's basically taking the Witch and making a hero from it.

It would be a giant witch thinger. Summoning BOTH walking and flying skeleton troops. As you upgrade, more troops get raised from the dead in addition to more health and dps.

Ability is raise hero. When used fallen heroes are revived with minimal health. As the ability advances in level, the heroes are revived with more % health restored. Perhaps at max level the heroes are restored their ability for a second use as well.