The original Challenges of Clash Royale are the Ever-present Event Challenges that you can find at the very bottom of your Events tab. These challenges are divided into 2 types, Classic and Grand.
Each battle won contributes to your final rewards with the maximum amount of wins being 12. Losing 3 battles will boot your from the Challenge but rewards are granted to all competitors, even if they don’t win any battles!
10 Gems to enter, top prize of 2,000 Gold and 100 cards
100 Gems to enter, top prize of 22,000 Gold and 1,100 cards
Matchmaking in Challenges is based on your number of wins! Keep in mind, all cards and Towers are capped at level 9 so that everyone battles on an even playing field.