An easy fix here could be that mobs only take falling damage if a player knocks or pushes it over the edge, which seems like it would be a valid way of killing something. But that would still leave the case of them not being able to follow you up a slope. You'd think most enemies would just run back to their spawn point or something in that case. Hopefully they make the AI be more like a player though, like it gauges if it can jump down and just pop a bandage to keep after you. So far pretty interesting.