First of all you need to get your mum to get her cat checked and if he can't find anything medically wrong that would be coursing him to do this then ask to be referred to a pet behaviourist and make sure its one that deals with cats more on a day to day basis.There are many things you can do to help him stop biting a clawing your mum and I could go into some but I really think it would be best if your mum saw a behaviourist as they will come to your mums house and see the environment the cat is living in and what he does everyday and be able to put a plan together to help him stop. It won't be a quick fix and will take time to re solve this problem and it will probaly be quite costly to but it will be worth it in the end. The other thing your mum could do to get some tips is read the vicky halls books.Good luck. If at the end of the day your mum still doesn't like his behaviour and can't cope then make sure she finds a rescue that will be prepared to put the work in.
Above all there is always a reason for a cat to act this way e.g because its in pain,because its un happy about something,because people thought it was funny when kitten bounced when they wiggled there toes and fingers and laughed teaching kitten it was perfectly aright to do so when kitten got older they do the same and of course kitten gets much bigger with sharper teeth,The cat is scared of something,Wants attention and has learned this is the best way to get it etc etc so before anyone thinks of putting there cat to sleep always think of this before you do so.

__________________