Murdaw is one of the early major antagonists you'll face. He has two forms. His first form is a straightforward physical attacker. Focus on keeping your HP high with Nevan's healing spells. Carver and the Hero should be your primary damage dealers. Ashlynn can use offensive spells like Frizz or Sizz. Murdaw's second form is more dangerous, often using disruptive spells and stronger physical attacks. He is weak to certain elemental spells (often Fire or Ice, depending on the version). Prioritize debuffing his attack with Sap or lowering his defense with Kasap if you have those spells. Keep your party's HP above 50% at all times, and be prepared for a sustained fight. Ensure your equipment is up to date before challenging him.
While Murdaw represents an early difficulty spike in the sixth entry, You can revisit this iconic confrontation through the Tickington sidequests in Dragon Quest XI S: Echoes of an Elusive Age.
While Murdaw serves as a pivotal boss in this title, he also appears as a powerful Rank S monster in Dragon Quest Monsters: The Dark Prince.