I got my creature just after I hit level 13, and didn't have too much trouble. The black ring soldiers north of there were challenging in groups on at level 12, but if you avoided them I don't think it would be terribly difficult to get the creature about level 10. It would help if you knew where you were going, perhaps keeping to the river to avoid opponents, but I don't recall what level the undead were in the mine, that you need to defeat to get the crystal skull.
