Thanks for the feedback! ❤️
B: Yeah those definitely need some work as their drawback is (or can be if unlucky) very dangerous. I've been thinking of either only allowing them to spawn on edges of the map or making them not destroy the tile after use.
C: The heretics do not spawn randomly but on the space where you open the heretic chest after you've moved away from them. Unless of course you've come across some weird unknown glitch where they break this rule.