A charmed sack is an item used while training at The Nexus. It can be claimed by talking to Ysondria, or by right-clicking her and selecting "Get charmed sack". It is used to store some of the corruption of the Grotesque and then emptying its content into a bowl on one of the pillars.
Initially, it can hold up to 15 corruption at a time, but after purifying enough corruption, it gains the ability to hold up to 18, 22, and eventually 25 corruption at a time. It retains this property after being destroyed and reclaimed (although all contents are lost). Partially filling the charmed sack will give a partially full charmed sack, while completely filling it will give a full charmed sack.
The following messages are displayed as the sack gains capacity:
The Nexus shudders. Your efforts have turned the creature back.
The sack will now hold 18 corruption.
The power coming from the Nexus is changing - your aid is weakening the creature.
The sack will now hold 22 corruption.
The Nexus is waning, you are close to defeating this monstrosity.
The sack will now hold 25 corruption.