Magnar the Bloodthirsty is the first arena boss. Wielding a Gladius and a heavy Shield, he is not to be underestimated despite wearing nor shirt nor chest armor.
Magnar deals pure slash damage, which can go fairly high with strength bonus.
As long as you wear slashing-resistant gear, you will be fine, though due to the nature of the Arena, you will want the best slashing-gear to avoid taking damage.
He is weak to Bludgeoning damage. Use a good weapon to finish the fight quickly.
Not to be confused with Ragnar the Cruel.