Draugr

In Old Norse sagas, a draugr arises when a powerful or malevolent person refuses to stay dead. The creature remains physically in its burial mound, growing supernaturally strong and heavy. It could leave the mound to crush livestock, drive people to madness, and kill those who disturbed it. The Eyrbyggja Saga and Grettis Saga record the most detailed accounts, including wrestling matches between heroes and draugar.

The draugr appears as a bloated, dark-blue or black corpse of immense size and weight. It retains the weapons and treasures buried with it. The stench of decay precedes it. Some draugar could shape-shift into animals or wisps of smoke to slip through keyholes.

Superhuman strength — a draugr could crush a man and his horse. Could drive people to madness through the 'draugr-ride' (sitting on a sleeper's chest). Could change size, turn into smoke, and enter buildings without opening doors. Some draugar possessed prophetic knowledge and could control the weather.