(i) The merman king says:
"'...to us, these waters are now banned. For us, the light will always blaze and the bell will toll and the words will curse until the Weird of the World.'" (p. 15)
We should simultaneously hear:
a Latin exorcism (see here);
a tolling bell -
- and see:
the houses of the merfolf city, Liri, rocking and crumbling;
the crystal dome shattering into bright shards;
a fisher boat with a chanting priest, the tolling bell and a blazing light.
(ii) "'Westward, maybe to Vinland or beyond. Whole vast realms of nature, Faerie, and man must be there, untouched by Christendom, open for our adventuring...we might become gods.'" (p. 256)
From "Westward..." to "...adventuring...," we should see the merfolk swimming at speed (see image). While hearing "...we might become gods...," we should see the coast of North America.
In a film trailer, the blazing light at the end of (i) could fill the screen, then fade to be followed by (ii).
(The linked exorcism is of a person but we only need to hear the opening words: "Exorcizo te, omnis spiritus immunde..." etc.)