Royal challenge becomes an option as a daily task once you have reached lvl 30 and one of the rewards is azurite which is very precious indeed.
The armies required for the royal challenge are huge, they also need to be high tier but there are deviations from the “guideline” amounts that camel have published.
Example, my troop power is 400000 below the stated amount to achieve 5 waves and yet I am still achieving 5 waves. A higher tiered army does make a difference.
I have been at the other end where I exceeded the requirement for 4 waves by 200000 power but was still only finishing 3 waves.
The guideline amounts are as follows
you must complete the royal challenge at least once a day and try to do so when you have all army available or immediately after recruitment (higher power of troops collectively)