How do you kill Monoliths??

[Master Shake]

Anything can be taken down with Disintegrate. It has a ridiculously low fatigue cost (10 for a D2 mage, 5 for a D3 mage!), so a couple death mages can cast it over and over.

I had 4 Abominations that were GoR'd with antimagic amulets, for a total MR of something like 25, all taken out by disintegrate during a single siege of an Ermor castle with 5 Dusk Elders, a Wraith Lord, and a D6 pretender inside. They just slammed Disintegrate into the Abominations over and over, and each one sucumbed eventually. Fail one MR check and that's it.

Another nice anti-SC spell is Petrify, which paralyzes if the MR is made (destroys if it is not).