Kuudra Believer

The Kuudra Believer waits by the Plhlegblast Pool once you have beaten Kuudra, asking for coin donations from those who believe Kuudra will return. Donations are never refunded, and a few specific donations do something:¹

4,202,022 coins while a Plhlegblast is within 3 blocks: Herring the Fish.
1 million coins or more, then entering Kuudra's Hollow within 30 minutes: the Weird Sailor appears.
A set amount after you have the Wet Napkin, again with a Plhlegblast close by: the Kuudra Follower Helmet.