Greater Transmutation (5e Feat)
From D&D Wiki
Prerequisites: Intelligence, Wisdom, or Charisma 13 or higher
Upon taking this feat you learns the spell true polymorph
You also gain the ability to cast true polymorph with a range of self once per long rest.
Note If mistakenly used to transform into an object or if maintained for the full duration in a form incapable of providing spell components you will be stuck. To restore your form you would require another individual capable of casting dispel magic, true polymorph, or using other such magic.