For Nippopolis is a side mission in the video game, "South Park: The Fractured But Whole".
Plot details follow.
Bring Gerald a Cheesing Vial.
After unlocking the Fartkour Buddy Power, go to SoDoSoPa. On top of the rundown building, you will see a pinwheel. Use inspection mode on this object in order to Fartkour to the top.
Here, you will find Gerald. In order to bring him back to reality, you will need to offer a Cheesing Vial. If you do not already have one, go to Kyle's House and find one upstairs in the attic.
Give him a Cheesing Vial to finish the quest and unlock the Cheesing Gerald summon to use in battle.