Just a suggestion, but the inclusion of player levels would be an interesting addition.
Could encourage challenges that increase the XP awarded to a player level.
Examples would include winning x matches with X comic.
Complete three matches in a day.
Win with only dark avengers or complete a second playthrough of the prolouge.
All the while, rewarding your frequent players who achieve certain levels in the game.
For example, player level has reached 20. Now when they complete a match, they get a 2x muliplier applied to the amount of ISO they won in the match.
Level 40 is awarded a 100 HP.
Level 60 gets a legendary comic (IW?)
These are just suggestions, but adding this feature will add an overall since of accomplishment and achievement. Something that can be lost in the current status of the game when someone feels their only progression was one comic and that comics functions have been modified beyond what they imagined.