217: Both of Percy’s first kisses resulted in subsequent explosions that nearly killed him. When Annabeth first kissed him at Mount Saint Helens, he triggered a volcanic eruption, freeing Typhon. When Rachel first kissed him before he and Beckendorf left for the Princess Andromeda on a mission, they blew up the enemy ship with a Greek fire explosion, which caused Beckendorf’s death.
218: Magnus Chase’s initials are MC. Those initials can also stand for the words main character, which Magnus Chase also is, the titular main character of his series, Magnus Chase and the Gods of Asgard.
219: In both the Norse and Greek pantheon, there is an Underworld goddess who can manipulate the dead, is seemingly split down the middle in the colors black and white, and utilizes emotions, being Hel(a) and Melinoe respectively, both met by the main character.