IIM Shillong does not have an OBC reservation due to some state laws. The minimum marks required for shortlisting OBC candidates is the same as the General Category, which is 75/75/75 in the VARC, DILR, and QA sections. The minimum percentile required for shortlisting may vary depending on the candidate's undergraduate stream.
For example, a male engineer would be in competition with other male engineers, and the minimum percentile required would depend on how well candidates from that category performed. As a general rule, a percentile of 98+ would be a safe bet for GEM candidates to receive a call, while a lower percentile may be sufficient for candidates from other streams.