The Demon Lord is a daily Clan Boss that your clan can attack, and with enough damage, take down to get resource rewards on a consistent basis. This is one of the best ways to accumulate resources in the game and should definitely be a priority to get a good team up and running.
During the progression phase of your account, you will want to attack the difficulty where you can both get the maximum chest for that difficulty, and your clan will also help you kill that difficulty. For this reason, it is very beneficial for you to be in a clan that is comparable to your level of Demon Lord capabilities so that you all work together help each other progress consistently.
End game players in the most optimal clans, will kill Ultra, Nightmare, and Brutal every single day, but it is common for some end game clans to just take down Ultra and Nightmare while leaving Brutal behind because Sacred shards and Legendary Skill Tomes cannot be obtained in Brutal.
After it was discovered how the Turn-Meter calculations work, there was a development within the community of building Unkillable Demon Lord teams which can be a great way to get into those last difficulties as soon as possible. Our friend Deadwood Jedi has amazing resources covering all sorts of these compositions to help you theorycraft based on your account over on his website!
The expected daily average of resources for an end game player in an optimal clan killing Ultra and Nightmare every day is:
*values slightly rounded
Silver: 123,000
Gems: 17.37
XP Brews: 23
Rare Tomes: 0
Epic Tomes: 0.51
Legendary Tomes: 0.34
Ancient Shards: 1.13
Void Shards: 0.42
Sacred Shards: 0.4
