Bain just started interviewing at my school (non-target in the Midwest) in the last few years, and I decided to attend a practice case info session at the business school put on by two consultant alums. During the info session I volunteered a ton (probably answered 75% of the questions, and luckily with pretty good answers) and afterwards I made an effort to meet both consultants, introduce myself and put a face to my name. I submitted my resume to the applicant pool, and I was called the following week by one of the alums who I met with to inform me they'd like to bring me in for a first round interview. Not sure how much of a difference it made, but I definitely think it helped taking the time to attend the info session, actively participating, and making a connection and strong impression on the recruiting contacts from the start rather than just hoping my resume would get noticed.
First round consisted of two 30 minute cases, pretty much zero behavioral. I actually felt really pessimistic leaving the interview, and even called some friends and told them I didn't think I would be advanced to the next round. I was taking a nap the afternoon of the interview when my phone rang, with one of the consultants who interviewed me inviting me to a final round office interview in the near future. Goes to show you want to stay calm on the outside even if you feel like you're struggling and totally lost with a case. In between the first and second rounds, I reached out to the alums I initially met at the info session, and between them and some of the ACs on their teams I was able to go through ~8 live practice cases over the phone with different Bain employees. Can't stress enough how much this helped me prepare.
Second round was three 30 minute cases with a partner and two senior managers, as well as a 30 minute behavioral/fit interview with a consultant. Saw two private equity due diligence cases, the key to these is looking at the overall market, then the competitive landscape, then the client's specific product offering and how it compares to the rest of the industry. I would definitely anticipate a few cases of this sort if you plan on interviewing with Bain. All the cases were pretty straightforward, pretty structured where the interviewer had several slides with key information which they would provide if you asked the right questions. After the final interview I kept anticipating a call, as I'd heard that top firms will often extend offers the same day as the interview. When I didn't hear I was somewhat nervous, but I did my best not to think about it. I received an offer a week later over the phone.