Mort Dinner Rick Andre

According to the bonus content for the episode, Mr. Nimbus was set to appear in a previous season but the episode was later scrapped. The writer team loved the character, so they ended up incorporating him into this episode.

Mister Nimbus and his "Nemesis" relationship with Rick is a major retcon, considering Rick and Morty have been in the ocean on Earth so many times before without Nimbus appearing or even being mentioned. A significant example is The Ricklantis Mixup (2017) from Season 3, where as a misdirect the episode focuses on the rebuilt Citadel Of Ricks while the show's primary Rick & Morty travel to Atlantis, complete with scuba gear and returning wet and leaving puddles on the floor. Being IN the ocean is certainly more than being ON the ocean in Rick's car.

References Psycho (1960)