The Tenebrous Ephemera will add a strange and eldritch glow to your Warframe, and small motes of energy will float off the surface as you move. It’s a fun look, and will undoubtedly add a strong flavor to your FashionFrame game.
To get the Tenebrous Ephemera, you will need to do a bit of grinding. Little Duck, the secretive agent you can find in the back room at Fortuna, is willing to sell you the Tenebrous Ephemera, but she wants something in return. It will cost you 15 Anomaly Shards to get her to part with this particular item.
To get Anomaly Shards, you will need to track the Sentient Anomaly in Veil Proxima, home of some Railjack missions. The Anomaly will appear roughly every two hours and will occupy one node in the Veil Proxima region for 30 minutes.
During this time, you will need to play the mission on that node, find the Sentient Ship that is causing the Anomaly, and board it. You will need to finish the mission and kill twenty Sentients on board the ship. The Anamoly Shard is a guaranteed reward from completing the Sentient Ship, so while there is some grind the RNG has been removed.
Little Duck has more than just the Tenebrous Ephemera; she also has several Captura Scenes that you can purchase for 10 Shards each. Just go to the back room in Fortuna, switch to Operator mode, and interact with Little Duck. At the bottom of the menu, you will see the “Exotic Goods” option. Click on this, and you will be able to purchase the Tenebrous Epehemra or the Captura scenes.