The theme for Diablo III's Season 26 is called Echoing Nightmare, and it's an "optional and rewarding end-game challenge where players fight within the memories of Nephalem who fell in a Greater Rift". A new activity that sounds like a pure challenge mode where players must "stand their ground until they are inevitably Overwhelmed or defeated".

It arrives as part of Diablo III Patch 2.7.3, which will hit the PTR this weekend. How players access the new Echoing Nightmare activity will be familiar to players in that they'll need to collect a Petrified Scream from a Greater Rift boss to gain entry. Throw this into Kanai's Cube and it will summon a portal leading to the new activity.

Here's the breakdown.

Petrified Screams and the Echoing Nightmare can only be accessed with seasonal characters.

Only one player is required to transmute a Petrified Scream to open an Echoing Nightmare in a multiplayer game.

Similar to a boss encounter, all players in a multiplayer game must accept a prompt to enter.

While within an Echoing Nightmare, the difficulty scales as players progress in the encounter. Players can progress faster by defeating monsters quickly.

Players receive the following rewards upon completing an Echoing Nightmare: EXP, Legendary Items, Blood Shards, Gems, and a new Legendary Gem, Whisper of Atonement.

The Whisper of Atonement is a Legendary Gem used exclusively for Augmenting Ancient Legendary items. It drops pre-ranked based upon player's performance in the Echoing Nightmare.

And with this Blizzard is also making changes to Greater Rifts with a chance for one to roll as Orek's Dream - which is described as "dreamlike rifts [that] have a curated list of maps and monster compositions". The pool of Greater Rift maps will change too, with Fields of Misery, Desolate Sands and Briarthorn Cemetery being added and Sewers of Caldeum and Hidden Aqueducts removed. Also a bunch of the more powerful monsters and larger threats will offer up more progression and experience.

Blizzard note, "We wanted to improve the Greater Rift experience through quality of life updates, balance changes and addressing community feedback. We reviewed all of the maps and monsters that appear in Greater Rifts and reworked the probabilities overall to make sure players spend more time with the content they enjoy. Less spaghetti and more chickens."

Elsewhere Patch 2.7.3 makes changes to Barbarian, Crusader, and Monk sets and items - so head here for the full Patch Notes.