I think there is potential to add some weekly/monthly challenges to the game.
Idea: Weekly Challenges that come with different Affixes
Core: List of different Affixes available and go on a mixed rotation every week. Each affixes have a 'difficulty value', depending on it's difficulty or what it does.
List of possible affixes:
(Affixes - difficulty value - description)
Enemies:
Fortified - 2 - All enemy units gain 20% armor equal to their health
Well Fed - 3 - All enemy units gain 30% Health
Zombified - 3 - If enemies unit die, it will be revived as a zombie
Critters - 3 - Critters may appear
Reviving - 4 - All enemies revive once with 50% health. Excess damage do not count
Immunity - 4 - All enemies will be immune to the first instance of damage. ( Eg, Troopers double shot ability would only count the second shot damage)
Boss - 5 - An enemy will have twice the stat and damage
Last Stand - 5 - When an enemy dies, if will buff the remaining enemies by 20%
Map:
Volcano - 3 - The map with have squares that will light units on fire. Each turn will take 10% health damage
Bombardment - 3 - The map will have squares that would be bombarded after 5 turns. Taking X amount of damage
Obstacle - 2 - The map will have squares that you cannot place any units on.
Jungle - 3 - You can only use Infantry
No Mans Land - 3 - You can only use Vehicles
Low Cost - 4 - Can only use low PvP value units