My idea is like all the mob spawned the overworld have like 5% of chance to be corrupted,with purple eyes and trying too kill you,turning pacive mobs into dangerous creatures.Which mob have a reaction if it turns corrupted:
If a sheep got corrupted its wool will turn dark-purple and its eye will turn like endermans eyes,it will chase and teleport to catch you.It drops corrupted wool.A bed made w/ it will transport you to a bonus dimension called Nighmare.
If a pig be corrupted it will chase and teleport to you,it hurts 2 hearts and drops rotten flesh.It have purple eyes too.
If a Slime be corrupted it will teleport and if dead will multiplicate 2 times more than a normal slime.It drop corrupted essence,that is used to make a corruption potion,used to corrupt mobs.
If a zombie is corrupted it will increase its speed and do the double of damage,its eyes is purple and it can teleport.
If a Skeleton is corrupted they shoting range will be larger and it can teleport,its drops corrupted arrows,that poison other mobs and have 10% of chance to corrupted the mob.