SpongeBob riding Mystery
Mystery is the sea horse SpongeBob adopted and let go in the episode, "My Pretty Seahorse." Mr. Krabs seemed to not like Mystery after SpongeBob lied to him about keeping outside but catching him when Mystery had a seizure. Her name matches because if she eats something and walks away, then nobody knows and it's a "Mystery" problem. For a while though, SpongeBob considered naming her "Grace," or "Majesty," or maybe "Debbie." She ate flowers, Krabby Patties, Old Man Jenkins, SpongeBob's spatula, all the Krabby Patties, the stove, SpongeBob's hat, SpongeBob's book chapter mark, and Mr. Krabs' money. Soon, Squidward had noticed it, and SpongeBob & Mr. Krabs were chasing her, and it's a "mystery" where Mystery is. Her sounds were provided by Frank Welker.