The Changeling race from Unearthed Arcana: Eberron has the Shapechanger trait, which lets it innately shapeshift:
As an action, you can polymorph into any humanoid of your size that you have seen, or back into your true form. However, your equipment does not change with you. If you die, you revert to your natural appearance.
Do you get the physical stats of the new form you hold? If you transform into the party's rogue, would you get its Dexterity? If I became an Aarakocra, could I fly?