Kra'gh is a Monster Set (Helm and Shoulder) available in light, medium or heavy armor. It drops in the Kra'gh (unique) style.
The 1-piece set bonus adds 1487 Physical Penetration.
2-piece set bonus: When you deal damage, you have a 10% chance to spawn dreugh limbs that create shockwaves in front of you dealing 1300 Physical Damage every 0.4 seconds for 2 seconds. This effect can occur once every 3 seconds.
The Shoulder can be acquired by using an Undaunted key on Maj al-Ragath'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 Fungal Grotto I which is part of the base game and located in Stonefalls. 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.