The Three-Headed Tusseladds' are Norwegian creatures with enormous sizes and heights comparable to the tallest trees. As they gain more age, they develop more additional heads. Since majority of them do have three heads, they are referred as three-headed giant trolls. Although, they can actually grow more than three heads where the limit is unknown.
In the Troll Hunter movie, Hans claimed that these gigantic monsters can have up to nine total heads.
Three-Headed Tusseladds are considered as "Woodland Trolls" because they dwell in the thick forest areas.
Again, on the film, when the crew went along with the troll hunter in the deep forest for the first-time. Several gigantic monsters suddenly chased them down and they were fortunately just lucky enough to have survive the attack.