I built you a test site with twenty different missions. There's no random here - every item can always be found in the same spot, every monster is carefully placed at its own spawn point. Only your tactical skills will decide the outcome! There is no RNGesus in outer space!
If you don't understand why you keep failing to beat the game, challenges will help you figure out when it's best to buy a few mage rings, or when upgrading a bonus health mutation might save your life.
And once you achieved great things in King of the Hill, then Challenges will serve as a place where you can run tests: in one of the challenges, you'll even fight my avatar in the second room of the level after you stock up on items and mutations.