Sulfer

A primarily aquatic monster, he most often found in lakes or rivers, but will occasionally tread on land, as he has both gills and lungs. He hunts large prey as most monsters do, whether shark or human. He is constantly on the move,  typically traveling through rivers, only moving on ground if the waterways a dead end. While he can survive on land, he hates staying up for too long, the unfamiliar exposure to air and varying gravity causes mild discomfort to him.
He is eyeless, so he greatly depends on his vibration sensors in his spines. He can detect even the slightest vibration in the water, but he has a much harder time on shore. His spines, very similar to a lionfish, are also equipped with a vemon that can cause stinging discomfort and exhaustion in brief doses, while extended exposure can momentarily paralyze a victim.
People, the ones who believe he's real anyway, say he was born white, but the blood of his victims permanently stained his skin it's crimson red. 

He isn't human-level intelligent but rivals that of the smartest animals, as he has brilliant problem-solving and analyzing skills. He does experience emotions, but his instincts greatly overpower them in any situation.