You have found the two objects that can revert two transformations!
However, not all transformation can be reverted by items you can collect! Four of them are reverted by interacting with other things you will find around.
Often, a small clue about how to revert the change is inside the description of the transformation itself.
I can assure you that all "basic" transformations (with the exception of the Minotaur) can be reverted before their
completion.
And for the Minotaur... If you get lost, the only thing that can get you out is some luck!
You can check the endings you have done in the section "Endings" of the menu. There are two possible endings for each monster you encounter, plus two "good endings" if you manage to defeat them all!