Most powerful spells?

[Graeme Dice]

Boron said:
Furthermore spelldescription states that it works only in own dominion .
So i wonder how useful this spell is all in all ?

It's a game-winner.

Swarm costs 1 nature gem but is 100 fatigue so the spell scripting ai should use more then 1 nature gem / swarm .

It doesn't tend to.

So you have the effect only in own dominion + either invest a lot of nature gems for swarm or have something like militia getting killed that you benefit from the spell ?

It's not just your troops that turn into manikins.

Is this really worth it when you can with zero gemcosts either spam false horrors or skeleton hordes ?

A dead dragonfly leads to a single manikin. When that manikin kills something, that also turns into a manikin. This snowballs very effectively. Two castings of swarm for example, can easily kill more than 50 devils, and probably much more than that.