User blog comment:Miskos3/Fairy Tail Chapter 391: Gray vs. Silver, Review/@comment-7418318-20140704072547/@comment-7418318-20140704090941

Back then we didn't really know what a Devil Slayer Magic was. It might just have been a similar name with a few similarities, but still something different.

Now we know that Devil Slayer Magic/Curse is exactly the same as Dragon Slayer and God Slayer Magic, only that it's more effective against different species.

And that's another problem. Instead of making it something interesting and different, it's just yet another Slayer Magic with the very same principles down to almost all of the details, down to the roar/bellow breath attack. The only differences seem to be how it's learned (from DS anyway, could still be the same as GS) and who it's most effective against.