Downloading Light in order to get mass Stone Skin is still possible, but in my opinion, if you choose Light, you need to give up some other magic, either Darkness – which is unrealistic – or Summoning, which is more likely. But I (I've said this twice now), if I have to choose between two 2% skills for a Necromancer, I wouldn't even go for Light. In the late game, Leadership (which gives tons of various units) and Luck are definitely 10 times more important than Stone Skin. P.S.: In my opinion, Light is practically useless except for mass Stone Skin and speed, and since Necromancers already have mass speed in attack, Stone Skin can be sacrificed (if you still get Light).