The required percentile to get into JBIMS varies every year and is dependent on the difficulty level of the entrance test. For OMS or all-India seats, the process is straightforward. You take the CET/MAT/ATMA/CMAT/CAT/XAT exams and apply with your score. Students who score high in CAT and XAT exams usually go to IIMs and XLRI, leaving students who applied with the remaining exams.
To have a chance of getting into JBIMS, you need to score a percentile of at least 99.98 in any of the exams. For Sydenham and Somaiya, a score of 99.95+ percentile is ideal, and a score of 99.9+ percentile offers you a fighting chance of being accepted.