The Altar of Alteration is a place where you can change a Witch's Talents or Appearance.

To change a Talent you will need 100 Diamonds and then with a bit of luck and you will end up with a more valuable Talent (same or more stars) for your Witch and maybe even a new Secondary Talent. But becareful, you could also lose a secondary talent.

To change a Witch's type/appearance you will need to do watch an Ad (or you can skip that if you have the VIP package). Doing so will randomly assign a new Witch type with a new appearance

You can perform either action as many times as you like so long as you have Diamonds or Ad Watches available.