User blog comment:B214/Chapter 497: The Winter Mage/@comment-5303512-20160808153824/@comment-1359322-20160808162122

You do realize that every single time there's a vs. in the title the fight will end in that chapter or following chapter right?


 * 1) Chapter 236 - Erza vs. Azuma, Chapter 237 - fight finish.
 * 2) Chapter 362 - Natsu vs. Jackal, fight end on the chapter.
 * 3) Chapter 391 - Gray vs. Silver, Chapter 392 - fight finish.

So the moment Mashima place Gray vs. Invel, the fight is determined to be finish in Chapter 499 at most.