On completion of Mission and defeating Super Villains players will get various types of resources which in other words could be called Treasure. Resources could be used to get powerful cards.
You need to collect six resources of same kind to get a card in reward. In the similar way you can make three sets of same resource. Each time to get a better cards.
Right now there are four kind of resources. More will be added as the game progresses. 
There is Storm’s Cape as a one of the resource. You need to collect six capes of different color like red, blue, green, purple, yellow and emerald. On completion of first set you will get a Storm Card. In the second set, a ISO-8 cards and in the third set another Storm Card.
Next is Suitcase which will give a She-Hulk Card, a ISO-8 Card and another She-Hulk Card on completion of three sets.
On collecting all the colors of sword of proficiency, another resource, will give you Taskmaster card, a ISO-8 Card for second set and a Taskmaster card for the third set.
Last resource for now is Assassin’s Choker which will give X-23 card, a ISO-8 Card and another X-23 card for the third set.
Will update the list when more resources are introduced.
Where do you get all 6 capes? I can only get 5 and it’s the same ones over and over again
Go for battle. Search for players who have the resource which you are looking for and battle with the player. If you win then in reward choose the resource.