Dead Planets
In some unfortunate cases, some planets get destroyed by external forces. Here's a list of all planets that existed at some point in the universe's history that no longer exist.
Planet Beetledeo
Planet Beetledeo was a planet that was inhabited by the Coleopturies in the Orino Galaxy. It was destroyed prior to the Universal War in 3510 UB by Speccio as their leader Spec was unhappy with the planet's decision to reject their rule. The destruction of the planet nearly caused the Coleopturie species to go extinct and many didn't have a home to return to. Many fled to planet Bugroo as refuge.
Planet Oxu
Planet Oxu was a medium sized planet in the Ceros Galaxy in the Yuxas System. It was another planet that was also destroyed at the hands of Spec and Speccio, for the same reasons: the sovreigns of the planet refused to submit to Spec's rule. The inhabitants, knowing the fate of Beetledeo began to panic immediately after and many fled the planet before it was destroyed by Spec.
The Oxu population also nearly went extinct after the destruction, but even moreso since Oxu was a smaller sized planet compared to Beetledeo. Now, it's still rare to see an Oxu on or off planet. The destruction of Oxu also led planets to band together and fight back.
Planet Quzolnya
Planet Quzolnya was the home planet of the Quzol, a centaur like species that were friends with the Novins in the early years of the universe. Their planet was suddenly destroyed by a black hole and much of the history and info about the planet was lost. However some bits and pieces about their language, their culture, and the appearance of their planet were saved and recovered from notes made by the Novins who visited. Without those, no one would have known about Quzolnya's existence and the demise of the planet.