M.Sc

See, nothing is good or bad, it's all about your interest and the field in which you want to see yourself growing and working. If you want to do this after graduation degree then move ahead because if it is your forte, you will do your best and ultimately, best will come out of you and you will do a splendid job and get success.
All the best.

Top colleges are:
Picasso International Animation VFX Gaming College, Lucknow and Arena Animation. To know about more colleges refer to the link: https://www.shiksha.com/animation/2d-3d-animation/articles/top-10-animation-colleges-in-india-blogId-10898.

Yes, AUCET is conducted for M.Sc in psychology. On the basis of the scores in AUCET exam, candidates are offered admission in Andhra University and its affiliated colleges.

It depends upon which course you want to pursue in mathematics. See, different IITs provide different Master's programs in mathematics. So you have to check the eligibility required for each of it. To check the eligibility criteria you can visit: https://www.eduncle.com/iit-jam-exam

Good question. M.Sc in mathematics deals mainly with abstract mathematics. Like modern algebra, real analysis etc. which has no real use in the life. On the other hand, applied mathematics deals with the mathematics which is used in physics, chemistry and engineering etc. In other words, used somewhere.

You can give M.MATH to enter ISI.

Yes, you can do it by given entrance exams: IIT JAM, JNU, CBEE, and any others universities like BHU, JNU, DU, HYU, etc.