STAR-format prompts with grading rubrics. Practice the conflict, failure, and ownership stories before the interviewer asks for them.
A random prompt, a timer, and the rubric the answer is graded against, plus the red flags that sink an otherwise good story and the follow-ups an interviewer is likely to ask next. Cards are drawn with spaced repetition, so the ones you miss come back sooner and the ones you know back off. Progress is kept in your browser.