Matamorphosis met·a·mor·pho·sis
Meaning: Profound change in form from one stage to the next in the life history of an organism, as from the caterpillar to the pupa and from the pupa to the adult butterfly.
Definition comes from dictionary.com
The word metamorphosis is a noun.
synonyms: mutation and transmutation
There is no past tense but it is plural met a mor pho sis.
That caterpillar went through a metamorphosis to change to butterfly.
A short boy was destined to be tall after experiencing metamorphosis
when the boy went through metamorphosis he was no longer the short boy, but the tall man.
This word would be best used when talking about great change.