Teeny tiny lil Galaxy
The Mushroom Galaxy is a small Galaxy that is home to 'Super' Mario, and no-one else really. Its planets mostly consist of creepy, mysterious creatures that are utterly hostile, and the fact that the Galaxy itself is so small (only a few hundred planets, if that) means that it is of little importance to the majority of the League. However, it is good for tourism, and also sporting events.
Sonic the Hedgehog also lives here.