I have an idea of adding another gameplay mode:
Boss Fight
It will be a fight to the teeth against an Uber-strong “boss” villain, surrounded by henchpeople…
Unique feature: The heroes will "rotate"
Explanation: The “boss” will be too strong for any single team, but anytime a hero got KO-ed, the game pauses to allow the player to specify a new hero to take the place of the fallen one. The other heroes still standing cannot be replaced.
Every 30 seconds, if the player hasn’t ended the “boss” yet, exactly 1 henchpeople will respawn. Thus, giving incentive for the player to actually send their best heroes first to thin out the enemy and helping survivability of the next team (contrast with CW, where invariably players will send their weakest team first).
WMD: Have another button to tap to launch a Weapon of Mass Destruction. The WMD will be a rare item but purchasable using diamonds (there, I’ve given you another way to monetize). A player can ‘collect’ many WMD to be used when their heroes are strong enough to go into Boss Fights, but only one WMD can be used per Boss Fight attempt, the WMD used during an attempt can only be chosen at the start of the attempt, and once used, no more.
Bonus Easter Eggs: If certain heroes happen to fight at the same time, a pop-up with their banter will appear.
This is just a suggestion/idea… not sure how difficult it will be to program.