Enchantment that does more damage to specific mobs

I know this is a somewhat duplicate but I can't understand what exactly to do. I'm trying to make an enchantment called Demonslayer, which does increased damage to all mobs from the Nether. My problem is that I can't figure out what code needs to go into the procedure, I have the enchantment rules and levels all set up, I just need the enchantment to do what it's supposed to do. Can someone just show me how to make a produce for an enchantment that increases damage done to specific mobs? Thanks