PSA: Echoing Hatred event (from Trace of Echoes drop)

I just got and used this but it's somewhat rare apparently so I thought I'd briefly mention what exactly it is. Note: this is exclusive to the LoH expansion.

A magenta (mythic-colored) "Trace of Echoes" might drop somewhere; I got mine from an undercity chest but I believe it can drop from anywhere. It does not show up in your inventory anywhere but instead starts a priority quest in Temis.

If you start it and enter the arena, no combat starts yet so you have all the time you need to prep / precast / snapshot, if your build warrants it. Then you click on a thing to start combat.

The difficulty you were in is completely irrelevant; the first waves start at "Hard" difficulty (obviously very easy) and then escalate. There are four one-time-use shrines: Channeling, Lethal, Artillery, and Protection. They all show up in the mini-map. Obviously you want to plan to use these, especially protection, before the run ends to last as long as possible.

Occasionally goblins show up very briefly and you have a limited time to kill them (just seconds or so) before they portal away.

My run ended while I was still fairly healthy; if you stop attacking for a few seconds or whatever, that seems to end it. (It happened for me when trying to walk to the last shrine.) I'm not sure it's even possible to die; I suspect it's programmed to also end as soon as you would have died, or it'd be completely useless for hardcore.

The loot is, or at least was for me, various random items and a ton of goblin loot bags. Each loot bag just contained charms/seals, temper manuals, horadric and crafting mats, and jewels. I did get a whole bunch of set charms.