Mid water-fighting, Elsa falls underwater where she encounters a blue-eyed horse made entirely of water, which appears in a flash of lightning before disappearing right before her eyes. The synopsis reveals that the horse is actually Nokk, "a mythical water spirit that takes the form of a horse and uses the power of the ocean to guard the secrets of the forest."
Typically Nokk serves as a sort of siren in the Germanic legends it originates from (how like Disney to use a dark fairy tale), luring folks to their deaths rather than being a guide, as Nokk seems to be for Elsa in the Frozen 2 trailer. But, we won't actually know if the magical entity is a friend or foe to our Queen until the movie actually premieres.
