This page explains how to complete the level 80 post-Shadowbringers quest "Deep Designs".
This quest is available if you have completed the quest An Old Friend.
Starting the Quest
Talk to Y'shtola in the Rak'tika Greatwood to begin the quest.
Speak with Tolshs Aath
Teleport to the Ondo Cups and go to the quest icon on the map. Talk to Tolshs Aath to proceed. There will be a cutscene.
Retrieve the Mnyiri Livers
Go northwest to where the orange arrow is pointing in the minimap. The destination is in a cave. The entrance is at Z: -1.5 and is surrounded by glowing blue coral. When you reach the orange circle on the map, go to the east part of the orange circle and check on the sparkling Bulbous Bag. There will be a cutscene.
Deliver the Mnyiri Livers
You can either teleport to the Ondo Cups or you can go southeast to where the orange arrow is pointing in the minimap. Talk to Tolshs Aath to hand over the Mnyiri Livers and complete the quest. There will be a cutscene.
Next Main Scenario Quest
After you complete the quest, talk to Urianger to accept the next quest: A Whale's Tale.