A quick guide on what seems to be the best possible prismatic trial seed for the Ethereal challenge.
This chest, right underneath the spawnpoint, contains a crowbar.
Grab the personal shield-generator.
The right one of the 2 red damage chests contains another crowbar.
Take the armor-piercing rounds.
Take the crowbar and the preon accumulator.
Try reaching the boss (Clay Dunestrider) in ~2:30 minutes in order to one-shot it with the preon.
Transform all your items, except the shield-generator into topaz brooches.
The printer will take:
- Armor-piercing rounds
Don't transform the generator!
The purple utility chest contains a rose buckler, take it.
This chest contains another topaz brooch.
Before activating the boss (1 overloading greater wisp, 2 blazing greater wisps), wait for your preon to cool down and then aim it directly at the overloading elite to prevent it from regenerating, rather than focusing down the blazing wisps, try sustaining your barriers by killing trash-monsters and get the occational hit in, for the most part you will want to try to let your preon take care of the boss.
After months of struggles, this seed finally helped end my nightmare.
I chose huntress to take the screenshots due to her utility skill, obviously you need to beat this trial as the Mercenary to achieve the challenge's goal.
I hope this "guide" helps atleast a little bit.