>>82879457Increase your combat levels, get your attack to at least 70 (preferably 75), defense to at least 65 (preferably 70 for barrows gear), ranged to 70 for black dhide, prayer to 60 for Chivalry (at least, Piety would be preferable but that requires 70) and get your magic as high as reasonably possible for the magic defense bonus.
Klause's fight is hard even with proper gear and levels, but you're definitely just trying to do it too early in terms of levels/items.
