Summoning the Grigoire boss in Diablo 4 is a surprisingly time-consuming endeavour, as you fight your way through Helltides to collect the special Living Steel material required to challenge him. The Galvanic Saint is one of the four bosses added in the Season of Blood as a new way to target farm Unique items, but gathering what you need to fight them is a task in itself.
While you can fight Grigoire on either Nightmare or Torment world tier, he'll only drop Shards of Agony—one of the materials required to summon the endgame Duriel boss—in the latter. With this in mind, it might be in your best interest to wait until you reach Torment world tier to fight Grigoire, just so you're maximising your rewards for time spent. Whatever you choose, here's how to get Living Steel and summon the Grigoire boss in Diablo 4.
Where to find Living Steel
You can get Living Steel during Helltides, but you'll have to locate and unlock a very specific chest to do so. The Tortured Gift of Living Steel chests are quite similar to the Tortured Gift of Mystery chests in that they look identical and don't appear on your map until you're very close to them. These chests cost a whopping 300 Aberrant Cinders and are guarded by an elite with a red bubble shield, which also makes them a little easier to spot. When you activate the chest, the shield will drop, and you'll have to defeat the elite before you can open it.
As with mystery chests, there are only a few possible locations these can spawn in a Helltide. The ever reliable Helltides website has a list of chest locations live during each event. Opening the chest will get you some Living Metal, but usually not enough to summon Grigoire, so you'll have to aim to open a couple. If you're on Nightmare world tier, you'll need two Living Metal, and five if you're trying to fight him on Torment.
How to summon the Grigoire boss
Now you've got your Living Steel, as the item description hints, you'll need to make your way to the Hall of the Penitent dungeon lair in the Dry Steppes. This is pretty easy to find since the icon appears on the map no matter how far you're zoomed out, similar to the capstone dungeon. If you're curious about what Unique items Grigoire can drop, be sure to see our Diablo 4 boss loot tables.
As you might surmise from his name, Grigoire has a lot of lightning-based attacks, so you'll also want to stack some Topaz gems on your jewellery for the extra resistance. Once inside, fight your way to the Chamber of Penitence and dump your Living Steel in the Light-Touched Altar to summon Grigoire and face the boss.
If you want an idea of what to expect, he's basically a giant Knight Penitent enemy in terms of his moveset, but with every swing of his mace he fires out a wave of little electric orbs. He'll also call down lightning strikes and summon lightning totems that create an electric maze partway through the fight.