Sniffing around for more of the less known myths and oddities, I came across the Sucuriju Gigante or Giant Anaconda. Whereas an Anaconda - the heaviest snake in the world - grows to about 30-35 ft the Sucurii apparently grows to way over 60ft in length. The Amazonian tribes also regard it ("her") as the being who created the Amazon. The pictures underneath was taken by a Colonel Rene van Lierde of one of these creatures.....from a helicopter.
The Sucuriju is basically described as a huge Anaconda that preys on the tribesman and large animals. It's a simple but cool concept for a controllable avatar in a game - put into the body of a huge snake-like monster, you can slither about in the undergrowth and rivers of some deep, dark forest, maybe gathering information and hunting prey when you get hungry (just a concept). It could be the more stealthy of your gaggle of monsters you directly control. I had an idea about the Jersey Devil - it being the offspring of a witch and such, it could be the magic-orientated character of your group and maybe reconnaissance as it's wings could come in handy for gliding and spotting enemies.
I don't have my game idea pinned down for definate yet, but these are just some quick thoughts.