Day-1:
Elephanta Island
Gateway of India
Taj Mahal Palace
Marine Drive
Leopold Cafe Day-2:
Juhu/Versova Beach
Band Stand
SiddhiVinayak Temple
Haji Ali Dargah
In Mumbai although two days will not be enough but still you can visit south mumbai-gateway of India,colaba causeway(best shopping & cheapest for clothes and jwellery)..
If you reach colaba early morning tou can take ferry to elephanta caves..this will be worth going..
Don’t miss the sunset at marine drive..the evenings or even if you have time at night just go there and relax for hours..
Then you may go to chowpati or juhu beach..
Visit Haji ali for spiritual experience..
If have time then also then explore around kalaghoda..the shops have heritage touch..walk to library etc..dm for details