Heart of the Night

Could you please tell me: I found the tear and collected the essence, who should I turn this quest in to, or what should I do next? It's impossible to defeat the demon. (I'm playing on an old version of the map).

Go to any of the garrisons around the city (after collecting the parts, it seems to mention this).

Regarding the "Empathy" skill: I personally don't see any major problems. A hypothetical Knight with a chalice, a half-set of mage items, and "Empathy" does the same thing without any additional conditions. In the case of Karlam, this even looks good conceptually - it turns out to be not only "mutual support" between units but also between the hero and the units. But the chance of it triggering can be adjusted if necessary.