Make your way to the lower left corner of Glastheim (P) and you will see Old Man Reiley (Located at 57, 111)
He will tell you a story and ask of you a favor before he passes on. If you accept, he'll ask for :
1x Marionette Doll
1x Singing Plant
1x Will of Red Darkness
After returning with these items, you will be given a Cursed Ring. Read the description on the ring to see the riddle.
As the clues in the riddle suggest, you must kill 5 Jormungandr, 3 Mermaid, and 1 Skoll Baby. You can kill them in any order, but take special note that you must have the Cursed Ring equipped when killing those monsters for it to count.
Upon killing the final monster in the list, the ring will automatically be deleted from your inventory and you will receive a Ring Des Nibelungen.
This quest is now complete.