Considering Infernal Hordes are the new activity in Diablo 4's latest season, it takes a little while to unlock them. Turns out that dropping into hell to fight wave after wave of the demonic host is somewhat of an endgame activity—who'd have thought it? Still, it's a fun new game mode with roguelike elements and it's pretty damn lucrative.

If you manage to weather every wave and gather a truckload of Burning Aether, you can dump it into a series of chests at the end of the activity for legendary items, rare materials, and even gold if you're bashing your head against the masterworking grind. Here I'll explain how to unlock the Infernal Hordes activity, how to get the Infernal Compass items you need to attempt it, and a brief rundown of how the whole shebang actually works.

How to unlock Infernal Hordes

The new season five activity isn't available until Nightmare world tier, so as your first step you need to complete the Cathedral of Light capstone dungeon on Veteran. You'll also want to start the seasonal quest so you can meet Locran. If you've progressed far enough, when you arrive in Nightmare world tier you'll find a quest called The Eyes of the Enemy with a marker in Zarbinzet. 

You'll need to complete this quest—helping Locran at Rakhat Keep—and then the To the Edge of the Abyss quest that follows. This sees you venture back into hell with the Triune scholar to face the Fell Council. Finish this and you'll get your first Infernal Hordes Compass and unlock the mode. These items are similar to Nightmare Dungeon Sigils, ie: you consume them in your inventory to start the activity, then can either warp directly there or enter manually at the gates of hell in Caldeum.

How to get an Infernal Hordes Compass and Abyssal Scrolls

Since the Infernal Hordes Compass is a consumable item that only lets you take part in the activity once, you'll need to acquire more if you want to keep reaping its extensive rewards. There are multiple ways to get them:

• Craft them at the Occultist: Just the same as Nightmare Dungeon Sigils, you can craft an Infernal Hordes Compass at the Occultist with Sigil Powder and Forgotten Souls. You can get the first by dismantling Nightmare Dungeon Sigils, while the second is a material from Helltides.
• Opening Helltide chests and slaying Doomsayers: You can get Infernal Compasses by opening chests with Aberrant Cinders during Helltides, plus by slaying Doomsayers. These are the NPCs you find kneeling in glyph circles during the event that you can speak to. They’ll generally transform into a monster, so simply slay them for a chance at a compass.
• Claiming Whisper Caches: Also similar to Nightmare Dungeon Sigils, opening caches at the Tree of Whispers has a 75% chance to drop an Infernal Compass
• Nightmare Dungeons and The Pit: Higher rarity Infernal Compasses also have a chance to drop from endgame activities such as Nightmare Dungeons and The Pit, so keep a lookout

There are eight tiers of Infernal Compass and while you can activate tier one in Nightmare world tier, you'll need to be on Torment to use anything higher. Any compass from tier three up includes affixes and a bonus chest for a guaranteed Greater Affix legendary. While higher tier compasses do have a chance to drop from endgame activities, you can also upgrade a compass using Abyssal Scrolls. These come from Helltide chests or the Spoils of Materials chest you can open at the end of an Infernal Horde.

So how do Infernal Hordes actually work?

The goal of the new Infernal Hordes activity is pretty simple: gather as much Burning Aether as you can, since at the end of the activity you use this resource to open chests and get loot. The structure is quite straightforward, though:

• Defeat enemies to summon Aether harvesting events: As you kill enemies in each wave, you’ll hear a bell ringing sound and see an icon appear on your minimap of the arena. This indicates an opportunity to harvest Aether. These are usually elites you can kill or mini events you can complete. Do them as fast as possible, grab the goods, and move onto the next.
• Choose an Infernal Offer after each wave: Each Infernal Offer consists of a Bane and a Boon. For example, you could summon the Butcher (Bane), but if you kill him he drops 25 Aether (Boon). These are the best way to boost how fast you harvest Aether and so too your rewards at the end. Think carefully when choosing.
• Head through the door to fight the Fell Council: Once all the waves are complete, you’ll have to head into the arena and fight the Fell Council boss. This selection of three demons is random, but you can usually deal with at least one of them individually since it’s a big arena.
• Spend your Burning Aether to open chests: The last step is spending your Aether. You can either purchase the Spoils of Equipment or the Spoils of Materials. The former gives weapons and armour, while the latter provides a random selection of mats, potentially including Infernal Horde materials like Abyssal Scrolls. Tier three Infernal Hordes and up also offer a bonus chest for 60 Aether that drops a guaranteed Greater Affix legendary. If you’ve got any Aether left after all that, you can also dump it into another chest to convert it into gold.

And that's the activity done. Rinse and repeat as compasses allow for lots of XP, gear, and gold.