but what can i do with spell like rule of burning iron or rule of gold if I haven't valid targets??
Alan the evil
Know your enemy. Armies that feature unarmoured or lightly-armoured units are less susceptible to the Rule of Burning Iron
, so if you're probably going to be facing a skirmisher-heavy forces - like <1,000 of Beastmen, Wood Elves, etc. - it's not your best missile. Likewise, the Law of Gold
shows its worth in games where magic items feature prominently - generally higher-points games in armies that feature powerful characters, such as the Warriors of Chaos. You wouldn't want to take the Law of Gold
against Daemons of Chaos armies, however, as you won't have any targets for it!
On a fair play note, you and your opponent probably look over each other's lists before play (and before spells are rolled); if you note a distinct absence of valid targets, swap that spell out for the lowest spell on the list. The 5+ spells are always at least a little useful, and fairly sure of going off.
he's doing a magic defense choice, so it could be better in my opinion taking dispel scrolls and magic missiles...
The scroll-caddy approach is a solid tactic, though more than one game I've seen both players try it and magic ends up doing nothing the whole game long. Still, in smaller games (<1,000 points) a Sorcerer can be a deciding factor, and the lack of being able to field a Lord choice means you need to adapt your strategy to cope. A Wall of Fire
, for example, can secure a flank for the entire game, or crush your enemy's headlong charge toward the center of your line.
I remember one time a lone Hero with the Armour of the Furnace was charged, fled through the wall of fire, and the unit that charged him was forced to pursue through the wall, destroying that unit. The Hero rallied next turn.