Well this was the first time I've seen this though the pioneering memorial of Deprimida Valley has a mission about it.
And yes, you are not blind, a fish in the outskirts of Deprimida Valley and looks like the other one at Bahama Marshland. And to tell you pioneer this one is hard to crack. Imagine this map boss walks fast and cast a huge AOE of curse that will surely slow you down and it is annoying. Not to mention Dream Blade Antelope has they same tactic.
If you see this guy around make sure you have a handful of people so your damage is progressive because his regeneration rate was quite fast.
So again pioneers, I'll keep you posted. Tata~