We are staying at Drancy (zone 3), and want to travel from there to the city center (1 day) by RER B and in the city by metro. Can we use Ticket Mobilis or need the Paris Visite? Can it be bought in advance?
3-zone Ticket Mobilis day ticket will work for Drancy - Paris. You can buy a Ticket Mobilis Paris Day Ticket in advance, but only in person at ticket windows and ticket machines. Ticket Mobilis becomes active upon its first usage in a turnstile / fare gate.