Spirit Release

Allows you to release your full power, taking on your true form for a short duration.

At 1st level you can use your bonus action to transform into your true form for 15 minutes,  use the stats, health, and items of your true form. Your equipment is absorbed into the form. At the end of this duration, you can choose to extend this form by five minutes if you succeed a Constitution saving throw. The DC is 10 + half your level rounded down. After the extended time, you take one level of exhaustion.

If you die in your true form, your sealed form takes 10 psychic damage plus any remaining damage. if your true form dies you can not use this ability again until for 1D3 days. 

After the time limit expires you can not use the ability until you take a long rest.

At 5th level, the duration is increased to 25 minutes.  At 7th level, the duration is increased to 45 minutes. At 11th level, the duration is increased to 1 hour and 30 minutes. At 17th level, the duration is increased to 3 hours. At 20th level, the duration is increased to 1 Day.