A Cosmosian reaches an intellectual maturity at the age of 15, and can live up to 2000 years, where they then fade from existence and their energy returns to the stars. 

You can speak, read, and write Common and Celestial

Cosmosians are usually 5 to 7 feet tall. The weight of dark matter is immense, but is partially stabilized within your form, settling on average at 400 lbs. Your size is medium.

Your base walking speed is 30 feet.

Your cosmic form enables you to absorb the energy needed to function, which allows you to go without traditional food or water.

Thanks to your cosmic origins, you have superior vision in dark and dim conditions. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.

Your body fluctuates with cosmic energy, allowing you to become immaterial and phase through objects. Twice a day as a reaction, you can cause a weapon attack that targets you to automatically miss. Alternatively, you may use this ability outside of combat to pass through nonmagical barriers (such as a locked door or wall) for 1 minute or until engaged in combat. Maintaining this state heavily taxes you. After using this ability, you must succeed a DC12 Constitution Saving throw or gain a level of exhaustion. 

Cosmosians can tap into the cosmic energy surrounding all matter and use it to bolster themselves. As a bonus action, you can increase your size by one factor for up to 10 minutes. If activated in combat, the additional stress on your form reduces the duration to 1 minute. Once enlarged you gain advantage on all strength checks and you gain temporary hit points for the duration. 2d6 at 1st level, 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level. Once you use this feature, you must complete a long rest before using it again.