Mighty Chudan is a Monster Set (Helm and Shoulder) available in light, medium or heavy armor. It drops in the Mighty Chudan (unique) style.
The 1-piece set bonus adds 2975 Spell Resistance and 2975 Physical Resistance.
2-piece set bonus: Adds 1206 Maximum Health. Gain Major Ward and Major Resolve at all times, increasing your Physical Resistance and Spell Resistance by 5280.
The Shoulder can be acquired by using an Undaunted key on Urgalarg Chief-Bane's chest. The Shoulder type, weight and trait are RNG based and can be from any dungeon this NPC gives Pledges for.
The Helm can be acquired from Ruins of Mazzatun which is part of the Shadows of the Hist DLC and located in Shadowfen. The Helm is guaranteed to drop from the final boss in veteran mode only. The weight and trait are RNG based.
You can mix-and-match Monster Set shoulders and helms from different sets and add two 1-piece bonuses to your build, or wear a complete set to take advantage of the full 2-piece set bonus.