Formless Body (5e Blessing)
From D&D Wiki
Create your own forms to become.
During any kind of rest, you can prepare a new body for yourself. This can be any size, any creature, and have any traits that make sense (DM evaluation). Three times per rest, you can switch to any of your forms. This might be awarded by any creature the possess the ability to shapeshift (such as a ancient dragon, deity, or other powerful being).