I am playing on Core rules. This is my first playthrough ever.

So i didn't know how to beat the black dragon in the elven city. I did it that way.

I had Aerie cast cloudkill on him (outside of his view range so he does not retaliate until he was 'badly injured'. On "Near Death' he fully heals himself.

So, i was not sure what to do. I tried killing him outright, but even with two bars of health he would butcher my party. So what i did was for Aerie to cast "incendiary cloud" on the dragon and quickly send Minsc in (who has the boots that make you twice as fast) to distract the dragon so that he doesn't heal himself. Lo and behold, the dragon was killed by the cloud!

I am quite proud of myself

That trick works in A LOT of encounters. Some groups will trigger and run at you, but a surprising number will just happily stand there going: "I wonder why my flesh is dissolving? That's a bit odd. But I don't see any enemies around, so I must not be in any immediate danger. I'm sure if I just wait here patiently things will sort themselves out..."

Also, two congratulations are in order: one for taking down the dragon and a second for spelling his name correctly. :-)