Which magic schools should I choose for the late game? Or should I go for a specific artifact?

I also wanted to know what advice you can give when playing as Razazak? Or in general, when playing as mages.
Well, I figured out that obsidian golems should be kept closer to the end of the battle, especially against Helmar, who likes to cast spells and other curses. And it's better to bring in steel golems into the battle more often. What else?