[Gregstrom]

Mind Hunt won't target friendly units, which makes it the killer of choice for stealthed enemies in your own territory. Beyond that, the target assignment is random.

Most assassination spells are the same, with the noticeable exception of Manifestation. I couldn't say about VoTD, come to think of it.

Arty spells mostly target *enemy* armies, but if more than one enemy army is in a province I would vaguely expect it to choose randomly. Crumble is an obvious exception, as it'll always hit a besieged army, and I have a vague idea leprosy goes for the beseigers.