Herr Magnus og bjærgtrolden ('Sir Magnus and the Mountain Troll') is a Danish ballad (The Types of the Scandinavian Medieval Ballad A 59, Proposal of supernatural woman rejected; Danmarks gamle Folkeviser 48).
It is attested in the nineteenth-century Denmark in only two versions, with three attestations, each of eight or nine stanzas. It is also found in Norway and Sweden.
Summary
A supernatural maiden (a mermaid in Norway and sometimes Sweden, or a female mountain being in other Swedish versions and in Denmark) tries to woo Sir Magnus by offering generous gifts. Magnus, however, rejects here; and in the Danish versions, he chops her into small pieces with his sword.
References
Herr Magnus og Bjærgtrolden Wikipedia(Text) CC BY-SA