User blog comment:FairyRaven/Fairy Tail Chapter 404: 00:00, Review and Commentary/@comment-3987368-20141011104106/@comment-25111584-20141011134320

It was just a joke on Raven's part, not Mashima's though ...

Mashima is hand-waving this, he just used Happy to officially announce that Erza is a Mary Sue (in battles anyway). Most probably we can expect this to mean that any Erza fights after this will also go down in a similar manner, I take this as Mashima telling us that they will. >.>