Rocky is a small guppy with a blue body and white fins and is unable to grow in size. Despite its small frame, Rocky finds ultravores palatable and even roars every time it eats.
Rocky is known to be associated with a number of bugs regarding its disappearance from a player's tank.
In one possible scenario, using Walter's ability on Rocky causes it to disappear from the player's tank. Otherwise, Rocky may disappear on its own regardless of care, emitting an explosive noise and indicating possible death. Rocky has been known to occasionally return while other cases claim Rocky is lost forever.
Because of it's tendency to suddenly disappear, Rocky has garnered attention in online communities where players speculate why Rocky disappears, what Rocky might be doing, and how to retrieve Rocky.