Monster types are chosen at random when starting the Echoing Nightmare, which can be to your benefit or detriment; some monster compositions will be more aggressive and/or favor ranged combat, making that particular Echoing Nightmare more difficult. Otherwise, the wave difficulty inside Echoing Nightmare scales somewhat similarly to Greater Rift tiers. Note that monsters inside Echoing Nightmares cannot be crowd-controlled with hard effects (Frozen, Stunned, Rooted or Knocked Back), invalidating certain builds (i.e., Krysbin's Sentence-reliant Necromancer builds). Soft crowd control effects (i.e., Slowed, Chilled) still apply. Monsters inside Echoing Nightmares do not drop items and, more importantly, do not drop gold. This invalidates cheesy tactics like equipping Boon of the Hoarder and Goldwrap to ensure invulnerability while doing them.