It works on the same principal as "Cloverfield": you only get glimpses of the creatures, since everything is being filmed by an unsteady hand-held camera. Hilariously, it posits the existence of a Troll Department, a secret agency within the Norwegian government charged with controlling Norway's troll population and eliminating those that get out of hand. The traditional Norwegian names ("tosselrad", "dovregubben" etc.) are used for the monsters.
It's all quite clever. It's amazing what one can find while randomly channel surfing.

