Soul Net

The NPC Alternative Rock will hand you this item after you offer him help. He needs you to capture evil spirits that corrupt the Deeplings.

You have to use this item on the corrupted deepling spawns, located east of the area accessed by a teleporter, in a cave populated by Deepling Workers. You need several people using Soul Nets to purify all the corrupted spawns before they "regenerate". This quest is probably related to an addon for the Deepling Outfits.