Will poor marks in 12th (around 68%) and a drop year have any affect on IPM IIM Indore interview?

Obviously, a low score may affect your interview but only a little. The key is to justify your low scores confidently and also answer any questions that are asked from your 12th syllabus.

Another way is to highlight your extra-curricular activities and achievements. Mention your other strengths but don’t lie about anything.

As far as the drop year is concerned I don’t think it will be much of a hurdle in your selection process because a major chunk of IPM students has taken a drop year. Still, you should be able to specify the reason for the same if asked.