Thank you very much for the detailed reply. While I had an inkling that the trade quest could be the domino that opens up the remaining optional content, I was simply too lazy to do four additional systematic sweeps, especially since normal NPC dialogue doesn't provide hints about potential trade partners. The rewards are worth the effort, though: Philosopher's Spirit and Unicorn Spirit are fantastic equipment pieces that can be considered a boon on higher difficulty settings in particular.
Yeah, when I said "RNG madness", I mainly meant "AI roulette" in this context. On higher difficulty settings, even against random mobs, most battles can be considered lost when one of the two party members falls. Enemies are usually faster than Elijah and Elise, and if all enemies (e.g. 3 random mobs) decide to use their AoE skills or to gang up on one party member, chances are that one party member falls before the party can even act, or the enemies inflict so much damage that the party can't heal in time, since next turn, the enemies get to act first again. This means wasting the first turn on offensive buffs is a surefire way to lose a battle. In some battles, I even had to resort to "pre-emptive healing" in order to win, that means using a heal skill even though the party is at full health, knowing that the enemies will have inflicted huge damage before the heal skill triggers. Normally, my gamer's pride doesn't allow me to play on anything other than the highest difficulty setting, but I guess composure comes naturally with age. :D
The enemy summoning portal is a very nice addition, though I suspected from the beginning that the 4 Holy Beasts wouldn't drop another AP treasure. :P
By the way, while I didn't encounter any bugs, I think it would be a great idea to rework the horse (River Valley) and chicken (Southern Valley) rescue sequences. When I rescued them, both times they were blocked by enemies. I thought the game had frozen due to the movement related issues, but the animals finally managed to make their way past the enemies after half a minute give or take. It should be possible to make the animal units "transparent" so that they can move through other units.
Thanks again for a great game and for your help! :)