You...want to join the Pumpcult?
Okay... But you must complete the initiation ceremony before you can officially join the Pumpcult.
You need to go look for Augusque (286,135), Edward (155, 200), and Cahan (441, 230). They are all friendly with our Pumpcult. Tell them the passphrase and obtain the keepsake.
Lastly, wear the Pumpcult's Halloween costume to prove your determination to join.
Come back and find me when you've completed all the steps for the initiation ceremony.
Be aware that if you leave this city, you will lose your qualification to participate in the initiation ceremony.