What are some fun things to do on the IIM Shillong campus as a fresher during or after class hours?

You’ve asked a very subjective question without giving much context so I’ll try to reason with you here and use a lot of ifs and thens. 

• The first few months on any campus would feel overwhelming with tonnes of submissions and no time for yourself. But once you’ve familiarized yourself with the routine you start to find things that suit your interests or find things that could help you groom yourself. 
• If you’re someone who likes being on your own and is looking for a moment of peace from the chaos and competition, you could apply for the non-academic clubs and committees at the campus. 
• Explore the campus and the local area around the campus. Go for a walk by yourself but again don’t forget the basics, be safe. 
• There are numerous mandatory events and conclaves organized by the different clubs and committees that nobody takes an interest in. Try to be mentally present in those events or make a habit of keeping notes for yourself in atleast 1 of every 3. 
• Start studying with different groups. Group study may not always bring the best results but it could teach you a thing or two. 
• Don’t forget to participate in case competitions and make submissions