Rainicorn-Dog Wars

The Rainicorn-Dog Wars refers to a war (or series of wars) between Dogs and Rainicorns. In "Her Parents," Jake explains that it was a conflict over territory in the Crystal Dimension that lasted for thousands of years. It is unknown exactly when it occurred, though it was apparently recent enough that a live Rainicorn (like Bob) would be able to remember it.

Based on Jake's drawing of the war and the photo of Bob Rainicorn with that a Dog saved his life, it seems that at least one of the sides had an air force of flying saucers, and the dogs used laser guns. These are forms of technology not seen anywhere else in the series so far, except for the Butterfly with laser gun from "The Other Tarts" who used a miniature laser gun to scare off Finn and Jake from the Anti-Gravity Tart Chamber and in the entrance sequence to the underworld in "Death in Bloom" where one can see some UFOs as they quickly pan down.

It is unknown which side, if any, was the ultimate victor of the war, though Bob and Ethel Rainicorn apparently still reside in the Crystal Dimension. It is unknown if any dogs do. The fact that Bob was saved by a dog and the two took a happy looking picture together but that Jake was concerned about lingering animosity may suggest that the war was not necessarily a conflict between all dogs and all Rainicorns, but perhaps some sort of internal Rainicorn conflict the dogs subsequently became involved in somehow. The true nature of the photograph is also questionable, because although both Bob and the dog appear happy, the dog is handcuffed.

However, because most of the information we have regarding this conflict/series of conflicts comes from Jake it might be exaggerated or inaccurate.

Trivia

 * In both pictures, there are UFOs in the sky.
 * In Bob's picture, it's shown that the dog that saved his life was handcuffed. But it seems the dog is smiling and waving when the picture is taken. Adam Muto has confirmed that the dog was captured, regardless of the deed.