Sentinel of Rkugamz is a Monster Set (Helm and Shoulder) available in light, medium or heavy armor. It drops in the Sentinel of Rkugamz (unique) style.
The 1-piece set bonus adds 4% Healing Done.
2-piece set bonus: When you heal a friendly target, you have a 10% chance to summon a dwemer spider that heals for 1049 Health and restores 524 Stamina to you and your allies within 5 meters every 1 second for 8 seconds. This effect can occur once every 15 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 Darkshade Caverns I which is part of the base game and located in Deshaan. 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.