A big thanks to Woolie Gaming (the king of RoR2) for this info.
- Right away, look for a Newt Altar. Finding one will get you a blue portal that enables you to get to the Lunar Bazaar.
- If you're attempting around when the Hidden Realms patch drops, you can find one in the Prismatic Trial near the spawn.
- Once inside the blue portal, turn around and jump off the cliff
- There will be an opening in the walls surrounded by a yellow mist
- Enter, and follow the tunnel to the very bottom
- You'll see a big pink portal. This will take you to the void realm.
- Inside, youll have to complete a series of 9 monster waves which start every time you activate a cell.
- Once you complete the last one, you'll unlock acrid! Congrats!
- You can activate multiple cells at a time, however difficulty increases drastically. Monsters gain items over time… So be sure you're ready, if you're going to attempt this.
- After you complete all the cells you can still return and keep doing the wave challenge once per run, and you'll get a red item instead of Acrid.