I am a shapeshifter is correct. Shapeshifter is a singular, countable noun. Such nouns must always be preceded by a word like a, the, this, that, my, etc. They can't stand alone. I am shapeshifter would sound like you were saying your name, e.g. I am Claire

* ✅ "I am a shapeshifter" is correct — "shapeshifter" is a countable noun, so use "a." * 💬 Ask like this: "Which is correct: 'I am shapeshifter' or 'I am a shapeshifter'?"