noun
metamorphosis
met-uh-MOR-fuh-sis/ˌmetəˈmɔːrfəsɪs/
A profound change in form or nature.
The caterpillar undergoes metamorphosis inside the chrysalis before emerging as a butterfly.

Etymology
The pieces express a change of form. Early English use especially described transformations by witchcraft, while the selected sense covers major changes in nature or appearance more generally.
In context
they transform themselves into this cocoon so they can go through a stage of change and metamorphosis
More examples
- A caterpillar's metamorphosis produces a butterfly with wings.
- Under new leadership, the team experiences a complete metamorphosis.
- The novel traces the remarkable metamorphoses of its main character.
Forms
metamorphosis · metamorphoses
metamorphose verb — To undergo or cause a profound transformation.
Similar words
- transformation
- Transformation is broader and need not suggest such profound change.
- conversion
- Conversion emphasizes a change in purpose, use, or belief.