This was probably my favorite feature out of different mods, and I completely understand if you guys don't want to do anything like this for your mod but I think you could modify the idea to make it fit nicely into your style.
I'm thinking that there's a chance that any mob that has already spawned could suddenly have glowing white eyes that track the player, but looking at it would return it to normal, like how Herobrine teleports. Alternatively, it could be more like a proximity thing where they return to normal when the player gets closer to them. The idea is similar to what can be found in the End of Herobrine mod, but with the stalker-only style that y'all have perfected.
#Possessed Animals and Mobs!
muted nimbus
I forgot to see if this was already posted and it was! Sorry!!!