User blog comment:Kogath/Monster Hunter 4 Ultimate for the Nintendo 3DS/@comment-1758220-20140623215019/@comment-25078123-20140624165047

Something that needs a rare subspecies? Diablos as mentioned in page 56 of the first Monster Hunter Illustrations book:

"The Diablos I saw was almost twice the size of the other male of its own kind that had mistakenly wandered into the Behemoth's territory. As the GIant DIablos circled the offender it's red Carapace shook with rage. I can still clearly recall how small the lost Diablos looked in comparison to this mighty specimen. No doubt the red giant was as a king among its kind."

The picture on that page shows a reddish diablos with black horns facing a normal colored diablos that had a broken horn (was the one horn Diablos the weaker one we have fought in unite?). Weither or not it's cannon, the One Horn Diablos quest did give us the red and black diablos set, so it's unclear, but there's my take even though I actually hate fighting diablos.

But, if anything, Brachydios should be getting a powered up version/subspecies similar to the other powerhouses (as much as I hate it, it'd make more since to have a powered up variant vs some random element Brachydios that lives in the desert or something.