Sometimes referred to by the Western magical world as the Black Basilisk, the Boiúna is a deadly magical snake found in the Amazon. Able to grow to huge lengths, they often coil through rivers in the territory they claim as their own. Surprisingly willing to share territory with other magical snakes and reptiles (including the Verdantmaw and Featherwing Dragon species, and the Mbói Tu’ĩ, Quetzalcoatl and Xiuhcoatl serpents) the Boiúna takes poorly to being attacked, and uses a curious magic to transfigure parts of their skin into other things, in order to help them fight the one who would do them harm.
Generally Boiúna are rarely seen, and keep to themselves, barring the occasions when the wish to reproduce, which happens once a decade or so. Rivers they are found in are often carefully skirted by Iara merpeople, and treated with great respect when they must be traversed. Indeed Iaras hold Boiúnas to such levels of respect that the bones of dead specimens are often carefully interned down the rivers they inhabited, and the skulls placed into special crypts in the underwater dwellings the merpeople make.
(Read about the mythical Boiúna Here. I hate that I have to include this but PLEASE DO NOT DELETE THE IMAGE SOURCE OR MY CAPTION.)