And, I must bring up the harpies again. SO annoying. They fly and throw stones. I come to get them. They fly higher so they can constantly get their +2 height bonus to AC and Attack.

What about making them what they are! Flying multiattacking claw slashing, club smashing melee brawlers who can charm you with their song and then fly down and bash you in the head. Instead, they fly and throw things at you, turning the entire battle into ranged fest or they make you chase after them. So frustrating.

I don't mind some variation, but a more true to 5e approach would really make that fight less annoying.

I mean, I get that you want to use the terrain in the fight. That's cool, but maybe there's some other way than having them constantly playing keep away rock throwers.

And the harpies would spread out their Luring Songs. Have one use hers. When enemies have snapped out of it, THEN another uses hers. A harpy can only charm you once, but you have to roll again for each new harpy's song.

So the harpies need to work together better. Should be first harpy sings, the others swarm in for the kill while those who failed are charmed. They focus on the PCs, leaving Mirkon alone because he's squishy and can be killed easier. They're more worried about taking out those who are charmed first.

Swoop down, bash with club and take with claws. Two hits per round. Now THAT would be a tough fight, and it wouldn't be all about chasing them around and trying to just get high enough so they don't get height bonus.