Dredge endings

The standard ending will be obtained if you complete all the tasks of the Collector and at the end of the game agree to go on a journey with him. But to get the best ending, you must sail south from Devil's Backbone and find the Old Mayor's camp on the island. Talk to him and he will tell you about the book, and also offer to contact the Lighthouse Keeper.

After that, visit Big Salt and talk to the Overseer to ask her about the scarlet book. Once you've done that, continue on with the Collector's errands. When you bring the last relic from Devil's Backbone, refuse to follow instead to the place of the ritual. Speak again and take the book from the Collector. Having done this, return to the Overseer and agree to her terms. Swim to the indicated place and throw away the book.