One thing to try is an indirect attack approach.
Basically this starts to come into its own when you get charged bolts.
This spell chains lightning bolts one after another, so it can easily clear rooms by itself, except for lightning immune mobs.
The thing here is that with the right positioning you can kill mobs without ever having a line of sight to most of them.
When you combine this with burst of speed, you can burst, dig, charged bolts and wall of stone the entrance again, if too many remain to handle safely.
Most of the time this is overkill as you can clear most rooms fairly quickly but it shines on tough rooms you still want to try.
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