ToME: the Tales of Maj'Eyal

I am having the same problem but with a goblin or orc called Aganor the Guardian who can only hit me on 9 of the tiles in the room (making me assume he is on the middle tile) but no amount of sun infusions nor chance on hit to cause damage will kill it or make it visible.

I was reading the Unlockables thread and saw someone mention power leveling in the Old Forrest and was wondering how you go about that. At a guess I'd say it probably had something to do with the Honey Tree's and letting Bee's spawn there and killing them, but I wanted to make sure.