The best interview prep you could do is review the history of EY BAS applicants on this website.
BAS went through rapid growth about 3 years ago, hiring in mid-level partners and directors from IBM, Accenture, and CGEY with the lure of a quick promotion. They brought their own warm and cuddly attitudes towards staff management and development with them (a brutal up or out approach)
Since then BAS have had to shed a lot of good folk, and F&PM in particular have quietly shoved out an awful lot of people.
Add to this that BAS don’t get any of the large sexy jobs that the likes of KPMG or Deloittes do, and you can see that EY BAS is not a good place to be in any part of your career.