You could change it so during Challenge events the matching color Bosses are effected.
During Challenge events reflect yellow event, all Season 1, and Season 2, stages with a yellow Boss give +50% loot and are -1 World Energy and a unique enemy would drop colored coins, 100 coins would allow a Challenge event summons.
During Challenge events reflect yellow event, they would drop yellow coins that could be used for the Guardians summons.
Example
1.12-9 has a yellow Boss, so during reflect yellow ( Guardians) it would be +50% loot, 3 we and a chance of a clockwork mob that drops yellow coins for use in the summons.
Summons Token
This seems boring.
Maybe they could add a hard mode just to the Elite mob stages?
As a reward, the first time you complete them it gets a silver Daily summons token for normal and a gold Epic Hero token for hard.
Example
Completing 1.23-6N would give a silver Daily summons token while 1.23-6H would give a gold Epic Hero token.
Completing all Season 1 hard stages would give you a Commander Grey avatar.
Otherwise 2.6-9N at 3 we is still champ for Recruits per World Energy, 2.15-8H is still champ for Recruits per loot ticket and 2.1-4N is champ for kit/ backpacks.
Even at 1.0 we for 1.8-7, I would not purchase world energy. My phone would overheat worse than for AR.
How do you figure? All of 2:1-xN gives the same backpacks, and all of 2:1-xH also gives the same backpacks (Hard being higher backpacks outside AR, and normal being higher during AR)
I like 2:1-2N or 2:1-3N and 2:1-7H and 2:1-8H as the levels tied for best recruits respectively in normal and hard as a general preference, although 2:1-9N has more monsters if you want a higher monster count and slightly more XP but fewer recruits.
Still used to ignoring kits/ backpacks ( pre Advanced House ). I will have to go over the numbers for 2.1. Looks like I recorded some numbers for Hard, when I was actually running Normal. Dang.