Case study with a current PA. The case study starts out simple but progresses in complexity as more edge cases are thrown in to test your mental framework. I managed to arrive at the correct answer for each question(there is a correct answer for every question despite HR telling you cases are open-ended). You are not allowed to make mistakes in your thinking or say something that is wrong even if you correct your thinking later and achieve consensus with the interviewer. Therefore make your first answer count.

3 rounds of case studies. Cases are very different from each other and mostly tests how you think. Not super mathematical or brain-teaser, and there probably isn't a systematic way to prepare. It's more a conversation about the way you think than a set list of questions.