So, let me see what we have so far.
At our disposal:
-a handful of people for regular tasks
-an airstrike
-good stealth
No:
-somehow getting into the house without the mage noticing, then assassinating him
-->too risky
-
Plasma Sphere,
Alpha and Omega, probably
Thermal Spear
-->too 'loud'
-
Flight
-->too obviously magical
Yes:
-Scouting the town for hidden monsters
-->we have confirmation that Cerys can sense them, so she would recognize their shapes if there are any in town
-->if there are none, we can proceed much more smoothly
Ideas:
-have something in the mage's house overheat to create a 'natural' fire to flush him out
-force him to leave to his underground base outside of the village to have an easier time fighting
-increase his body temperature from afar until he dies
I seriously don't understand why we don't just go look for a house with a scrant and an adult male in it since that combination will probably mean the male is the Mage. Then use thermokinesis from outside to raise his temperature afifteen degrees (centigrade) or so. He'll be dead within a matter of hours and he'll most likely be delirious and have difficulty focusing enough to accomplish anything of worth in the mean time.
Send the enforcers to go find and clear out his base we're at it.
We already know which house it is... and from how Rukia described the effects of our manipulation before, raising the temperature by a few degrees should be enough to kill him in moments.
