This guide will help you to understand how to unlock Acrid.
How to Unlock Acrid
Where to Find the Void?
First of all you will need to travel to The "Bazaar Between time". Simply enter a blue portal to enter this zone. You can also spend lunar coins to spawn a Blue portal 100%.
Once you are there you will want to jump down into the chasm below. There will be a mine shaft with yellow light glowing through it. Enter that mine shaft to find the portal that will take you to the void.
Entering the Portal
So once you've entered the purple portal you will find yourself in the void.
There will be 9 beacons that you can interact with to slowly release Acrid from the prison. The whole zone sort of acts like you are drowning under water. You will slowly lose health if you are not standing in the air pocket created by interacting with the beacons.
You will have to active the beacons 1 by 1 and some require a fair amount of mobility to reach. During the interaction the enemy types that will spawn will increase. Another interesting thing of note is the fact that the creatures also get to use items. These will be randomly chosen during the event.
Once you have interacted with the last prison the enemies will have acces to one Red tier item to buff them. It can be quite tricky to manage them if they get a good item. Once you've managed to charge the final object you will get the achievement unlocking Acrid.
And here's your reward.