Hey there,
I entered MHS in 2015 through Year 10 entry (graduated this year) so I may be able to help you a bit!
In terms of the application process, they will ask for your past two school reports which is probably your term 1(?) year 9 report and your term 4 year 8 report (I think it was like that for me). They will also ask that you record all of your co-curricular and extracurricular activities and awards along with copies of them for validation purposes.
The most important part of this process though is definitely the application/interest letter. I firmly believe that this is what the assessors (both of which I know as they were my teachers) will value the most. As long as your report is decent (that is, above average) and your entrance exam result decent (at least 1 superior) then it is likely you will make it into the interview process. For my year, about 60 from 300ish made it into the interview process, 30 of which were accepted into the school.
In terms of the interview itself, I remember it lasting for 1-2 hours? The majority of that time is spent as a group of around 6ish. You will talk about real-world issues, how they can be addressed, then split into two groups and undertake problem solving puzzles to test your teamwork and communication skills. The last 10 minutes is spent in a private interview with both teachers, where they will personally question you about your goals and really make you reflect on yourself. Remember to smile, crack jokes (not too many) when you can. MHS teachers love humour.
Personally I entered with a major focus on Sport (with a bit of music and decent academic records), specifically athletics. I didn't really have any records with leadership as I was in general an introvert/quiet kid during middle school. (but it does help)
As for tips..
-Keep up that table tennis, if you have any awards from school, throw them in!
-same with badminton
-Probably should try to do an exam for Violin. A certificate will really help. MHS music talent really cycles from good to dry, and with this cohort leaving I gotta say we've entered the dry period again. Good music records will help you in your application. If you are really grade 7 ish Violin, you'll be good enough for Camerata which is really appealing especially as a new student.
-For your application letter, put as much emotion as you can into it. Make it personal. Don't sound like a robot. e.g. I wrote a story about how I went from a hopeless kid who could barely run 200m without dying to a state athlete. Pretty cheesy.
-don't worry about swimming haha i still can't swim :^)
-Really push yourself in the interview. Show them that you care and are able to think in an open-minded manner. Show them that you can reflect upon yourself.
That's all that I can think of so far. If you have any additional questions, feel free to PM me and I'll try my best to answer them!
Good luck