Echoing Nightmare

Echoing Nightmare is a gameplay element in Diablo III, introduced in Season 26.

Gameplay
Echoing Nightmare is an endgame activity, where players fight within the memories of nephalem who fell in a Great Rift. The player has to stand their ground until they are overwhelmed or defeated. The combat is wave-based, taking place on a relatively small map with four shrines at the start. The difficulty scales as additional monster waves are spawned. The faster monsters are killed, the quicker the player's tier level increases.

To unlock the Nightmare, players must collect a Petrified Scream from defeated Great Rift Guardians. Transmuting a Petrified Scream in Kanai's Cube summons a portal that players can enter to face the horrors of a nephalem's past.

Petrified Screams and the Echoing Nightmare can only be accessed with seasonal characters (note that the character must be level 70 to open a nightmare. 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. The monsters inside a Nightmare don't drop gold, items, or health globes.

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

Development
Inspiration for the Echoing Nightmare came from Orek's words in regards to Nephalem Rifts, that "many nephalem have stood where you are now, but few succeeded in overcoming the trials." The Nightmare explores what happened to the nephalem that did not succeed.

In May 2022, it was announced that Echoing Nightmare would be a permanent feature of the game.