Is it possible for an average student to crack the AIIMS in Delhi?

You need to understand that entrance examination do not test your knowledge. It is also not in place to select meritorious students. Entrance exams are there to eliminate students. 

Anyone who is in the top 100/200, mostly kave the same knowledge. The entrance actually tests your MCQ solving ability. It’s not about knowing every answer. It is rather about eliminating the wrong answers and making a good educated guess. 

You don’t need to master every subject to score well. Figure out a strategy that works best for you. It does not matter whether you get a Physics question right or a GK question, you will get the same marks, so play to your strengths. Practice as many previous year questions as you can. Also, if you can’t figure out a particular question, leave it. Strategize well and practice hard and you can definitely crack AIIMS entrance.