The tournament mode was introduced on the 3rd September 2017.
It was announced with the update on 31th September 2017, in shape from a countdown.
There are two different tournaments, with different enter costs & prices.
Grand Tournament enter costs are 10 and 100 from the Master Tournament.
You need 10 wins to complete a tournament.
You can get these prices: chests, medals, new stickers, tournament points and you become all gems what you spent on the tournament back (if you complete a tournament)!
and 100