User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-6050823-20140107011913/@comment-11112316-20140110061703

Certainly, MH info is often exaggerated and the legends that surround many of the creatures often don't ring completely true; but the Fatalis does have incredibly remarkable abilities - even by MH standards - and drying up areas like The Deserted Islands could be fairly feasible when you consider the sheer longevity of the Fatalis. While we don't know just how long their lifespan is, given from what we information we can garner from the White Fatalis, a Fatalis could have all the time in the world to ruin an ecosystem. As to why a Fatalis has yet to shown such drastic abilities? From what can be gathered of their behavior, Fatalises do seem to be monsters with long periods of 'inactivity' - as in, they'd rather stay in one area for a long while rather than travel a lot. In my opinion, the Fatalis is simply a species that has the power to destroy vast areas of the realm, but simply chooses to stay in one location primarily.

Given some thought, it would not be impossible for a creature to theorectically exist that can challenge and even surpass the powers of the Fatalis; but I still stand that such an assertion is a bit of a strech considering how conspicuous a powerful Fatalis is. If such a creature existed, I just imagine it would have been noticed by now. Then again, Dhisufiroa is an incredibly powerful dragon and its existence was not known for quite some time, so you have a point there. The Guild keeping the creature a secret is also not implausible.

Of course, if you want to consider the series from an outside context, I don't feel Capcom would really shake the status quo and reveal a monster that can surpass the Fatalis.