Grigoire, The Galvanic Saint is a Endgame Boss.
Grigoire, The Galvanic Saint (World Tier III and IV): You must gather enough Living Steel from the Tortured Offering in Helltide. In addition to Unique items that can only drop from Grigoire, you also have a chance to receive the Demonbinder Mount Armor Cosmetic.
Keep in mind that: You’ll need to meet the summoning conditions of a boss each time you want to fight it, so hold on to any additional summoning materials that you might acquire during your travels.