loot system should meet the following basic criteria:
1) Encourage people to spend time in the game. So the reward should not be too generous, especially in view of the system of daily awards. Because collecting all the cards, many players leave the game.
2) The award shall depend on the complexity of the card. The easiest method is to bind to the complexity of the number of players on the map.
3) The award shall be a valuable person should enjoy receiving cards. Many people wish for months to get this or that thing in online games. There should be a similar principle. Can not months, but days should leave.