As noted in the sectional flowchart for this Chapter, you’ll not see a Hotspot on this area from the NavMap on the Celsius.

When you enter, go along to the destination pointed out by the red arrow on the minimap. This will lead to the entrance of Mushroom Rock, where you’ll see Shinra plant another CommSphere. A cutscene should also start, after which you should go to the north part of the area. Use the lift there to reach 2,000 Gil and head to Djose on foot to trigger a 100%-critical scene with Gippal. That’ll be as much as we cover in the Mushroom Rock part of the walkthrough…

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Let Shinra put down the CommSphere (left) and then head towards the red marker. Return to Djose to speak with Gippal (right) afterwards.