As a member of the old Supercells, do I need to register again?
All accounts from the old Supercells have been transitioned to the new Supercells. As a member from the old website, you can simply sign in using your old Supercells account. The first time you sign in, we will confirm certain key details of your registration. For security purposes, we strongly suggest that you change your password when you re-confirm your account with us.
In addition to your username, several other key items have been transitioned from the old Supercells. You can find more details on what was transitioned from the old Supercells on The Old Supercells help topic.