Developing a Necromancer hero.

Up there, something was mentioned about Necromancers not needing skills that lead to the "Scream of Terror" spell; I don't know, I liked all the skills. "Banish" is also a good skill, especially if the opponent is a summoner or a demon. "Dark Regeneration" and "Master" are the only two skills that seem unnecessary. I took almost all the skills up to that special skill, except for "Dark Regeneration." Instead, I got "Firestorm" and "Mind Control," and that's it. I reloaded the game three times to get the experience. Does anyone know what the percentage chance is of getting "Dark Regeneration"? I'm playing as Markel in the original campaign, meaning it's a mod of the original in "Tribes of the East."