Quote Originally Posted by Alukah View Post
I still believe there's more to that, like balance issues. But either way, what exactly is a killer effect? From the OP I thought it would mean a damage increase.
Example, if you're a dragoon with 'Dragon Killer' effect and you fight Dragon type enemies, when they're targeting you there's a chance you'll intimidate them, which in XIV terms would basically be 'a chance for a 1-2 second paralyze effect' which will give you breathing room. So it's not HUGELY useful, but it for tanks and the like, depending on how SE would have handled it, it can be useful for mitigating tons of damage in the long run.

The other effect is the Blue Mage version which raises/lowers your damage against certain family of enemies, it's, as stated, a type of 'elemental wheel', only in regards to you vs monster families.