One word.
One impostor.

Choose a category to reveal its clue. One clue is an impostor. You can guess before opening any. After a wrong answer, open another clue to guess again. Each category adds 1 to your score; Reveal few letters counts as 3 clues and is never the impostor. Your score counts hints, not submitted answers. Once all six clues are open, keep guessing without a limit. Use Reveal answer to give up.