Trolls are continuously hungry and can eat insanely large amounts of food. Their favorite food is sheep. They live well away from humans. Sun will turn them to stone. Water trolls like to live under bridges or in mud marshes in or near freshwater. When a troll moves in, it dredges it's new home so that it can sink down deep away from the sun. They can hold their breath for a long time. Trolls can speak the language of where they live and are good at word games. Trolls have good hearing and smell.
* photo courtesy of Arthur Spiderwick's Field Guide