Survival not hard enough? Hostile mobs too boring and simple?
I've got you, with hostile variants; Now *most* hostile mobs have got different types they can become, some times just armor, weapons and potion effects, some with special abilities. Some like the zombies work together, others like skeletons are dangerous alone.
Can you survive a world with these new challenges, death around every corner?

currently altered mobs:
zombies (normal, husk, drowned, villager)
skeletons (normal, stray, wither_skeleton)
spiders
phantoms
enderman (no variants, just more scary)