Skills:
1) glyph of lesser energy
2) meteor shower
3) mist form (elite)
4) bed of coals
5) frozen burst
6) inferno
7) rotting flesh
8) optional, isn't necessary if you execute the sequence properly.
I whipped up this build by myself, although it took a while. Basically it should kill all trolls in about 20 secs if executed properly. Once you're in the cave, wait until all of the trolls are grouped together tightly. Cast glyph of lesser energy then. Target the closest one to you (press C), and run just close enough to get the whole mob to chase you. Right when you see them run for you, cast meteor shower. By the time it casts you'll have about half or more of your hp bar gone, but that's fine. After that its very simple, just use the rest of the skills in order: mist form, bed of coals, frozen burst, inferno, then rotting flesh. They all have to be linked together very quickly or they wont die.
Basically you'll use bed of coals, which will make the trolls catch on fire every time they get hit with a meteor from meteor shower. then frozen burst will make it difficult for them to run away from the bed of coals. Inferno will add alot of extra damage, then disease them so they all have 9 degen (burning + disease). And with mist form you'll be invincible the whole time!
If something does happen to go wrong and the trolls dont die, just run around a bit till you can use mist form again and finish them off. This build Does take practice, but you should be able to kill them all in about 20 seconds.
This is a tested build, and has got me 5 skills points thus far, i hope it works for you too,
EDIT: Attributes (with runes) are:
12 fire magic
11 water magic
11 energy storage ( i think, should give you 70 max energy with a +10 energy staff)
1 Death magic
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